Table of contents for issue 2, volume 997, The Astrophysical Journal

Blind discoveries of millimeter-wave transient events in nontargeted surveys, as opposed to follow-up or pointed observations, have only become possible in the past decade using cosmic microwave background surveys. Here we present the first results from the SPT-3G Galactic Plane Survey—the first dedicated high-sensitivity, wide-field, time-domain, millimeter-wave survey of the Galactic Plane, conducted with the South Pole Telescope (SPT) using the SPT-3G camera. The survey field covers approximately 100 deg² near the Galactic center. In 2023 and 2024, this survey consisted of roughly 1500 individual 20 minute observations in three bands centered at 95, 150, and 220 GHz, with plans for more observations in the coming years. We report the detection of two transient events exceeding a 5σ threshold in both the 95 and 150 GHz bands in the first 2 yr of SPT-3G Galactic Plane Survey data. Both events are unpolarized and exhibit durations of approximately 1 day, with peak flux densities at 150 GHz of at least 50 mJy. The peak isotropic luminosities at 150 GHz are on the order of 10³¹ erg s⁻¹. Both events are associated with previously identified accreting white dwarfs. Magnetic reconnection in the accretion disk is a likely explanation for the observed millimeter flares. In the future, we plan to expand the transient search in the Galactic Plane by lowering the detection threshold, enabling single-band detections, analyzing lightcurves on a range of timescales, and including additional data from future observations.

Gravitational waves (GWs) accompanied by electromagnetic counterparts, known as bright sirens, provide a novel methodology to measure the Hubble constant (H₀). However, the rarity of such multimessenger events limits the precision of the H₀ constraint. Recently, the newly discovered class of nuclear transient, quasiperiodic eruptions (QPEs), shows intriguing evidence of a stellar-mass companion captured by a supermassive black hole in an extreme/intermediate mass ratio inspiral, which is the most promising source of space-based GW detectors, such as LISA. Here, we model the secular orbital evolution of known QPE systems using two frameworks: a stripping scenario in which periodic mass transfer at periapsis drives the evolution, and an orbiter–disk collision scenario in which the companion interacts with a misaligned accretion disk, modulated by coupled orbiter–disk precession. For each framework, we assess detectability by LISA, together with the resulting constraints on H₀. Our principal findings are (i) in the stripping scenario, no currently known QPE reaches detectability within a four-year LISA mission; (ii) in the orbiter–disk scenario, two sources—eRO-QPE2 and eRO-QPE4—are detectable with signal-to-noise ratios ≃8.5–28.8 and constrain H₀ with a fractional uncertainty of 6.7%–14.9%. QPE systems remain uncertain on the decade-long secular evolution. Therefore, they motivate continued time-domain monitoring of QPE candidates.

The Compton Spectrometer and Imager (COSI) is a NASA satellite mission under development designed to survey the entire sky at 0.2–5 MeV with a wide-field gamma-ray telescope. Its main instrument is a germanium detector array surrounded on the sides and bottom by bismuth germanium oxide scintillator active shields (the “Anticoincidence Subsystem” (ACS)) to reduce and monitor background and for detecting transients. COSI will have an onboard trigger algorithm to detect gamma-ray bursts (GRBs) in the ACS and send data to the ground for further analysis. In this paper, we present three localization methods that we evaluated for the localization of short GRBs (sGRBs) using the ACS light curves. The first method is the χ² fit already used by the Fermi Gamma-ray Burst Monitor, which calculates the best fit between look-up tables and the GRB data. The second method is a maximum likelihood estimation fit implemented in bc-tools for the BurstCube mission that performs a fit between the instrument response function and the GRB data. The last method is based on deep learning techniques and consists of a neural network developed for the COSI mission and trained to perform a regression of the sGRB position, taking as input the count rates of each ACS panel. The localization errors obtained by analyzing simulated sGRBs with the three methods are consistent. Despite the theoretical similarity between the approaches, their consistency in results is noteworthy, as they differ substantially in their implementations and optimization processes. The bc-tools obtain the best localization accuracy.

We present a new analysis of the spectroscopic variability of WISE J104915.57−531906.1AB (WISE 1049AB, L7.5+T0.5), observed using the NIRSpec instrument on board the James Webb Space Telescope (GO 2965; PI: Biller). We explore the variability of the dominant molecular bands present in their 0.6–5.3 μm spectra (H₂O, CH₄, and CO), finding that the B component exhibits a higher maximum deviation than the A component in all the wavelength ranges tested. The light curves reveal wavelength-dependent (atmospheric depth) and possibly chemistry-dependent variability. In particular, for the A component, the variability in the light curves at the wavelengths traced by the CH₄ and CO molecular absorption features is higher than that for of H₂O, even when both trace similar pressure levels. We conclude that clouds alone are unlikely to explain the increased variability of CO and CH₄ with respect to H₂O, suggesting that an additional physical mechanism is needed to explain the observed variability. This mechanism is probably due to thermochemical instabilities. Finally, we provide visual representations of the 3D atmospheric maps reconstructed for both components using the molecular band contributions at different pressure levels and the fits of planetary-scale waves.

Quasi-thermal noise is an important diagnostic tool for measuring electron density and temperature in space plasmas, with its low-frequency range being dominated by electron shot noise. However, previous missions have shown that conventional shot noise models often yield poor fits in the low frequency , limiting the accurate characterization of electron parameters. To address this issue, we introduce an effective sheath resistance into the previous model, thereby establishing a calibrated shot noise model that improves measurements of electron parameters in the inner heliosphere. Methodologically, we applied the steep-descent and Levenberg–Marquardt method algorithm to determine the electron density and temperature above the plasma frequency; we then isolate the pure shot noise by subtracting other noise sources; and finally, we derive the antenna impedance using measurements below the plasma frequency (). Based on Parker Solar Probe (PSP) observations during PSP Encounter 4 ∼ 8 (with unbiased antennas operating in the dipole regime), we obtain an effective antenna capacitance of and an effective resistance in the range of 0.5 ∼ 4 MΩ, with their radial of the capacitances and resistances of and , respectively.

We present a new planetary structure/thermal evolution model, designed for use in problems that couple orbital dynamics with planetary structure. We first benchmark our structural/thermal evolution calculations against the MESA stellar evolution code, finding excellent agreement across a wide range of planet mass, equilibrium temperature, entropy, and extra heating deposited at various depths in the planet. We then apply our method to study the tidal migration histories of Neptunes in the recently identified “ridge” (periods ∼3–6 days), a feature that has been suggested to be populated via high-eccentricity migration (HEM) of more distant Neptunes. We find that it is difficult to form a circularized Neptune in the ridge without instigating runaway tidal inflation and likely atmospheric destruction; low-eccentricity Neptunes in the ridge can only be emplaced by HEM if they are metal-rich and exhibit finely tuned tidal quality factors. If follow-up observations confirm that low-eccentricity Neptunes in the ridge did arrive via HEM and are not strongly enriched in metals, our calculations indicate that their tidal heating mechanism must operate in the upper reaches of the planet to avoid runaway inflation. Gravity modes excited in upper radiative layers are a possible candidate mechanism, while friction in the core or turbulent dissipation in convective zones could be ruled out.

The “sub-Jovian desert” (2 ≲ R_p ≲ 10 R_⊕, periods ≲3 days) is sparsely populated but no longer empty. Recent surveys have revealed that planets residing in the desert are dense (ρ ≳ 1 g cm⁻³), massive (∼10−50 M_⊕), and orbit metal-rich stars that are indistinguishable from those hosting hot Jupiters. However, their origins remain mysterious. In this work, we adopt and test the hypothesis that tidal destruction of hot Jupiters can populate the sub-Jovian desert with stripped remnant planets. We first show that stars hosting desert dwellers exhibit Galactic kinematics indicative of an older population descended from those hosting hot Jupiters. We highlight that tidally driven Roche-lobe overflow (RLO) can indeed populate the desert with planets similar to those observed, but only if angular momentum transfer during RLO is inefficient (“lossy” RLO). The entire width of the sub-Jovian desert can be backfilled with the remnants of hot Jupiters that possessed their empirically inferred spread in entropy. In this picture, current desert dwellers such as LTT 9779 b should be tidally decaying at an observationally testable rate of ∼0.5 ms yr⁻¹. Our theory also predicts that desert dweller host stars may rotate up to an order of magnitude more rapidly than field stars; rotation period differences may persist ∼ Gyr after RLO. Lossy RLO may also manifest as a burst of IR excess that could outshine the host star for up to ∼10³ yr. If these predictions are confirmed by observations, our theory indicates that desert dwellers can be leveraged to study the interiors of giant planets in exquisite detail.

We report the discovery of a substantial sodium doublet (Na D λλ5890, 5896)—traced neutral outflow in the quiescent galaxy JADES-GS-206183 at z = 1.317. Its JWST/NIRSpec-Microshutter Array spectrum shows a deep, blueshifted Na D absorption, revealing a neutral outflow with and a mass outflow rate of . This outflow rate exceeds that of any neutral outflows identified beyond z ∼ 1 by the same line and is comparable with those in local galaxies with intensive star formation (SF) or luminous active galactic nuclei (AGN). JADES-GS-206183 is also a peculiar quiescent galaxy with a spiral+bar morphology, high dust attenuation (A_V = 2.27 ± 0.23 mag). Paschen α (Paα) emission from the FRESCO NIRCam grism confirms its low star formation rate (SFR_Paα = 10.78 ± 0.55 M_⊙ yr⁻¹), placing it 0.5 dex below the main sequence (). Despite the systematics introduced by different SF history priors, the spectral energy distribution modeling, combining Hubble Space Telescope-to-NIRCam photometry with the Very Large Telescope/MUSE spectrum, suggests that JADES-GS-206183 experienced an older episode of SF 0.5–2 Gyr ago and a possible rejuvenation within the recent ∼10 Myr. Moreover, rest-frame optical lines indicate that the current AGN activity of JADES-GS-206183, if present, is also weak. Even though we tentatively detect a broad component of the Hα line, it likely traces an ionized outflow rather than an AGN. The results demonstrate that the Na D outflow in JADES-GS-206183 is highly unlikely to be driven by current SF or nuclear activity. Instead, it may represent a long-lasting fossil outflow from past AGN activity, potentially cotriggered with the early phase of rejuvenation.

The search for sources of high-energy astrophysical neutrinos can be significantly advanced through a multimessenger approach, which seeks to detect the γ-rays that accompany neutrinos as they are produced at their sources. Multimessenger observations have so far provided the first evidence for a neutrino source, illustrated by the joint detection of the flaring blazar TXS 0506+056 in high-energy (E > 1 GeV) and very-high-energy (VHE; E > 100 GeV) γ-rays in coincidence with the high-energy neutrino IceCube-170922A, identified by IceCube. Imaging atmospheric Cherenkov telescopes (IACTs), namely FACT, H.E.S.S., MAGIC, and VERITAS, continue to conduct extensive neutrino target-of-opportunity follow-up programs. These programs have two components: follow-up observations of single astrophysical neutrino candidate events (such as IceCube-170922A), and observation of known γ-ray sources after the identification of a cluster of neutrino events by IceCube. Here we present a comprehensive analysis of follow-up observations of high-energy neutrino events observed by the four IACTs between 2017 September (after the IceCube-170922A event) and 2021 January. Our study found no associations between γ-ray sources and the observed neutrino events. We provide a detailed overview of each neutrino event and its potential counterparts. Furthermore, a joint analysis of all IACT data is included, yielding combined upper limits on the VHE γ-ray flux.

With the continued acquisition of high-precision tracking data by the Juno spacecraft, significant progress has been made in accurately determining Jupiter’s dynamical parameters. In this study, we utilize the orbit determination and gravity field recovery software SPOT, developed by Wuhan University, to process all available two-way Doppler tracking data of Juno’s perijove passes between 2016 and 2024. Incorporating 19 additional perijoves (PJ39–PJ68) beyond the 26 arcs used in the previous study, a joint estimation of Jupiter’s 40 degree zonal gravity harmonics, four tesseral degree-2 terms, spin-axis orientation parameters, and tidal Love number is determined. The results indicate that, compared with previously published Juno-based gravity field solutions, the accuracy of coefficients J₂–J₅ has improved by more than a factor of 2, while the J₁₃–J₃₆ terms exhibit an average improvement of about 30%. A stochastic force was introduced to absorb unmodeled small perturbations near perijoves, but its rapidly varying orientation does not point to an identifiable physical origin. The uncertainty of Jupiter’s spin-axis rotation parameter is improved to about 1 × 10^–7 rad, indicating no significant deviation between the principal axis of inertia and the rotation axis. The estimated accuracy of the static tidal Love numbers is improved by roughly a factor of 2 compared with earlier Juno-based tidal analyses. Due to limitations in orbital geometry, the satellite-dependent tidal Love numbers cannot be determined with sufficient accuracy to reveal potential dynamical tidal effects. This work provides improved dynamical parameters for constraining Jupiter’s interior structure.

We investigated the star formation history and stellar populations of a sample of 205 Type I quasar host galaxies (0.1 < z < 0.35) and compared them with normal (nonactive) galaxies of the same mass and redshift within the volume of the Galaxy and Mass Assembly redshift survey. We find that quasar host galaxies tend to be star-forming galaxies (∼80%) lying on the star-forming main sequence; the fraction of quasar host galaxies that are quiescent (∼20%) is lower than the fraction of quiescent galaxies in the comparison sample of normal galaxies (54%). We find that the mean star formation rate (SFR) of quasar host galaxies has increased over the past 100 Myr by a factor of 2–3, but these galaxies were star-forming at all times previously. Our data are more consistent with quasar activity originating together with an increase in the SFR of otherwise normal galaxies, similar to episodic star formation in normal spirals. We argue that this indicates that secular processes and minor mergers may be the favored triggers of nuclear activity in the local Universe.

We demonstrate a novel setup for hybrid particle-in-cell simulations designed to isolate the physics of the shock precursor over long time periods for significantly lower computational cost than previous methods. This is achieved using a “faux-shock” or shock-like boundary condition on one edge of our simulation domain such that particles that interact with the boundary either pass through it or are reflected off of it with a change in momentum that mimics scattering in the downstream. We show that our faux-shock setup reproduces the same fluid quantities and phase spaces as traditional shock simulations, including those which could otherwise only be done in 3D, with higher particle resolution and for reduced computational cost. While the method involves an assumed boundary condition, it nonetheless captures the essential physics of interest, establishing it as a reliable and efficient tool for future self-consistent studies of instabilities driven by cosmic rays in a shock upstream medium.

Type IIn supernovae (SNe IIn) are a subclass of core-collapse SNe in which strong interactions occur between the ejecta and dense circumstellar material, creating ideal conditions for the production of high-energy neutrinos. This makes them promising candidate sources of neutrinos. In this work, we conduct an association study between 163 SNe IIn observed by the Zwicky Transient Facility and 138 neutrino alert events detected by the IceCube Neutrino Observatory. After excluding alerts with poor localization, we find two SNe that are spatiotemporally coincident with neutrino events. IC 231027A and IC 250421A coincide with the positions of SN 2023syz and SN 2025cbj, respectively, within their localization uncertainties, and the neutrino arrival times are delayed by 38 days and 61 days relative to the discovery times of the corresponding SNe. Using Monte Carlo simulations, we estimate that the probability of two such events occurring by chance in our sample is p ∼ 0.67%, suggesting that they may originate from genuine physical associations, though the result is not yet statistically significant. Our model calculations, however, indicate that the likelihood of a neutrino originating from IC 231027A is low, implying that the association between IC 231027A and SN 2023syz is likely coincidental. Nevertheless, under optimistic parameters, the probability of detecting a neutrino from the whole SNe IIn sample could reach ≳6%, indicating that detecting neutrino emission from the SNe population may be possible. Our study provides a systematic analysis, combining statistical analysis and model calculations, to assess whether interacting supernovae can serve as potential sources of neutrino emission.

In this paper we calculate the expected orbital elements, radiants, and velocities of Earth-impacting interstellar objects. We generate a synthetic population of ∼10¹⁰ interstellar objects with M-star kinematics in order to obtain ∼10⁴ Earth impactors. The relative flux of impactors arriving from the direction of the solar apex and the Galactic plane is enhanced by a factor of ∼2 relative to the mean. The fastest impactors also arrive from these directions, although Earth impactors are generally slower than objects in the overall population. This is because the Earth-impacting subset contains a higher fraction of low-eccentricity hyperbolic objects, which are more strongly affected by gravitational focusing. Earth-impacting interstellar objects are more likely to have retrograde orbits close to the ecliptic plane. A selection effect makes the inclination distribution of Earth-impacting interstellar objects uniform (sinusoidal) at low (high) perihelion distances. In turn, low-perihelion impactors have a higher impact probability towards the ecliptic plane. The overall impactor population therefore exhibits an intermediate inclination distribution between uniform and sinusoidal. In turn, low-perihelion impactors have a higher impact probability towards the ecliptic plane. The highest-velocity impacts are most likely to occur in the spring when the Earth is moving towards the solar apex. However, impacts in general are more likely to occur during the winter when the Earth is located in the direction of the antapex. Interstellar objects are more likely to impact the Earth at low latitudes close to the equator, with a slight preference for the Northern Hemisphere due to the location of the apex. These distributions are independent of the assumed interstellar object number density, albedos, and size–frequency distribution and are publicly available.

The nature of the obscuring material in active galactic nuclei (AGN) can be studied by measuring changes in the line-of-sight column density, N_H,LOS, over time. This can be accomplished by monitoring AGN over long periods of time and at all timescales. However, this can only be done for a few selected objects as it is resource intensive. Therefore, the best option currently is to focus on population statistics based on the available archival data. In this work, we study 79 Seyfert 1 and Seyfert 2 galaxies from the Million Quasars (or Milliquas) catalog to estimate a lower limit on the fraction of sources in the local Universe (z < 0.1) that display spectral variability among observations. We find that 43 sources (54% ± 11%) show indications of N_H,LOS variability at 90% confidence level. Interestingly, we also find that the variable fraction is similar for both Seyfert 1 (%) and Seyfert 2 (f_Sy2 ∼ 47% ± 15%) galaxies. The slightly higher f_Sy1 fraction could be due to either a physical difference in the obscurers or the higher data quality in the Seyfert 1 population. We also search for potential dependencies on the timescale between variable and nonvariable observation pairs within a given source. In agreement with previous studies, we find evidence that more variability occurs on longer timescales than on shorter timescales. We present the 43 variable sources as a promising sample for future N_H variability studies.

Accurate sunspot number estimation is essential for understanding the long-term evolution of solar activity and its impact on space weather. Sunspot numbers have been manually determined, leading to inconsistencies and observer-dependent biases. To address this, the World Data Center Sunspot Index and Long-term Solar Observations (WDC-SILSO) aggregates data from a global network of observatories to estimate the daily total sunspot number, enabling cross-validation and calibration across simultaneous observations. This study proposes a novel deep learning framework for automated total sunspot number calculation using solar full-disk continuum images from the Solar Dynamics Observatory. The method integrates U-Net for sunspot segmentation, K-means clustering for distinguishing umbrae from penumbrae, and You Only Look Once model for sunspot group detection. The selection of image-processing thresholds and neural network hyperparameters is optimized with respect to WDC-SILSO reference values during training. The results demonstrate a high correlation of 0.97 between the estimated and the WDC-SILSO daily total sunspot numbers. Furthermore, the framework offers a scalable approach suitable for future high-resolution solar observations.

We present results from the most sensitive all-sky search to date for continuous gravitational waves with frequencies 30.0 Hz ≤ f ≤ 250.0 Hz and frequency derivatives Hz s⁻¹. We deploy this search on the Einstein@Home volunteer-computing project and on three supercomputer clusters. At the end of a multistage approach there are four surviving candidates: three from “hardware injections,” i.e., signals “added” by moving the instruments’ mirrors, and one due to line disturbances in the data. The high sensitivity of our search enabled the first-ever detection of hardware injection 11. We set upper limits on the gravitational wave amplitude h₀, and translate these to upper limits on the neutron star ellipticity and on the r-mode amplitude. The most stringent upper limits are at 173 Hz with h₀ = 6.5 × 10⁻²⁶, at the 90% confidence level, which improve by about 70% with respect to the LIGO-Virgo-KAGRA Collaboration’s most stringent O3 upper limits, and might well be competitive with results from O4 searches.

Infrared-luminous galaxies are important sites of stellar and black hole mass assembly at most redshifts. Their luminosities are often estimated by fitting spectral energy distribution (SED) models to near- to far-infrared data, but the dependence of these estimates on the data used is not well understood. Here, using observations simulated from a well-studied local sample, we compare the effects of wavelength coverage, signal-to-noise ratio, flux calibration, angular resolution, and redshift on the recovery of starburst, active galactic nucleus (AGN), and host luminosities. We show that the most important factors are wavelength coverage that spans the peak in a SED, and dense wavelength sampling. Such observations recover starburst and AGN infrared luminosities with systematic bias below 20%. Starburst luminosities are best recovered with far-infrared observations, while AGN luminosities are best recovered with near- and mid-infrared observations, though the recovery of both are enhanced with near/mid-infrared and far-infrared observations, respectively. Host luminosities are best recovered with near/far-infrared observations, but are usually biased low, by ≳20%. The recovery of starburst and AGN luminosity is enhanced by observing at high angular resolution. Starburst-dominated systems show more biased recovery of luminosities than do AGN-dominated systems. As redshift increases, far-infrared observations become more capable and mid-infrared observations less capable at recovering luminosities. Our results highlight the transformative power of a far-infrared instrument with dense wavelength coverage, from tens to hundreds of microns, for studying infrared-luminous galaxies. We tabulate estimates of systematic bias and random error for use with JWST and other observatories.

The detection of very-high-energy gamma rays from M87 can provide crucial insights into particle acceleration and radiation mechanisms in jets. The recent observations by the Large High Altitude Air Shower Observatory detector extend the energy range of TeV gamma-ray astronomy, and also the variability study to the TeV energy domain. We have modeled the low state and flare state multiwavelength spectral energy distributions of M87 within a time-dependent framework. In our model, the low state gamma-ray flux results from the emissions from the subparsec and the kiloparsec scale jets of M87, whereas the flare state gamma-ray flux is mainly produced in the subparsec scale jet. We have shown that the spectral and temporal features of the TeV gamma-ray spectrum of M87 are consistent with this two-zone model, where the contribution from the subparsec scale jet significantly increases during the flare state.

The L/T transition is a critical evolutionary stage for brown dwarfs and self-luminous giant planets. L/T transition brown dwarfs are more likely to be spectroscopically variable, and their high-amplitude variability probes distributions in their clouds and chemical makeup. This paper presents Hubble Space Telescope Wide Field Camera 3 spectral time-series data for three variable L/T transition brown dwarfs and compares the findings to the highly variable benchmark object 2MASS J2139. All four targets reveal significant brightness variability between 1.1 and 1.65 μm but show a difference in wavelength dependence of the variability amplitude. Three of our targets do not show significant decrease in variability amplitude in the 1.4 μm water absorption band commonly found in previous studies of L/T transition brown dwarfs. Additionally, at least two brown dwarfs have irregular-shaped, nonsinusoidal light curves. We create heterogeneous atmospheric models by linearly combining SONORA Diamondback model spectra, comparing them with the observations, and identifying the optimal effective temperature, cloud opacity, and cloud coverage for each object. Comparisons between the observed and model color–magnitude variations that trace both spectral windows and molecular features reveal that the early-T dwarfs likely possess heterogeneous clouds. The three T dwarfs show different trends in the same color–magnitude space, which suggests secondary mechanisms driving their spectral variability. This work broadens the sample of L/T transition brown dwarfs that have detailed spectral time-series analysis and offers new insights that can guide future atmospheric modeling efforts for both brown dwarfs and exoplanets.

A merger origin has been suggested for M83’s massive, metal-rich extended H i disk and nuclear starburst. We observe M83’s stellar halo to test this idea. We train nearest-neighbor star–galaxy separation on wide-area Subaru imaging with Hubble Space Telescope data to map M83’s halo in resolved stars. We find that M83 has an extended, very low-density smooth stellar halo of old and metal-poor [M/H] ∼ −1.15 RGB stars with a mass between 15 and 40 kpc of . In addition to M83’s well-known Northern Stream, our ground-based Subaru imaging reveals a new stream to M83’s south, which modeling suggests could be its trailing arm. The combined stream masses are , with metallicity [M/H] = −1.0 ± 0.2. The stream progenitor was only recently accreted, as its stellar populations suggest that it formed stars until 2.1 ± 1.3 Gyr ago. M83 lies on the stellar halo mass–metallicity correlation seen for other Milky Way–mass galaxies, albeit with low stellar halo mass. We infer a total accreted mass of , with the most massive past merger having . We identify plausible M83 analogs in TNG-50 with similar stellar halos, finding that while a recent accretion can create a prominent stellar stream, such accretions do not trigger starburst activity, nor do they deliver enough gas to form M83’s extended H i disk. We conclude that other nonmerger mechanisms, such as secular evolution or accretion of gas from the intergalactic medium, are likely to be responsible for M83’s remarkable properties.

Recent observations suggest that Tycho’s supernova remnant (SNR; SN 1572) is expanding into a cavity wall of molecular clouds (MCs), which decelerate the SNR and influence its multiwavelength morphology. To constrain the physical properties of environmental MCs and search for heated gas, we perform a James Clerk Maxwell Telescope ¹²CO J = 3–2 observation and compare with previous ¹²CO J = 2–1, ¹²CO J = 1–0 and ¹³CO J = 1–0 data. We present the ¹²CO J = 3–2 map toward Tycho and show that the ¹²CO J = 3–2 spatial distribution and line profiles are similar to those of the lower-J CO lines. By comparing the multiple transitions of CO and the RADEX models, we constrain the physical properties of molecular gas surrounding Tycho: the northern cloud has a molecular column density of N(H₂) = 0.5–4.5 × 10²² cm⁻², while other regions have N(H₂) = 0.2–3.9 × 10²¹ cm⁻²; the kinetic temperatures T_k of these clouds are in the range of 9–22 K, and the volume densities n(H₂) are 20–700 cm⁻³. We also discuss the difficulty in finding hot molecular gas shocked by such a young SNR. We estimate that the shocked molecular layer can be as thin as 0.003 pc, corresponding to 02 at the distance of 2.5 kpc, which is 2 orders of magnitude smaller than the angular resolution of current CO observations. Therefore, our molecular observations are largely insensitive to the thin shocked gas layer; instead, they detect the environmental gas.

The core mass function (CMF) of prestellar cores is essential for understanding the initial conditions of star and cluster formation. However, the universality of the CMF and its relationship to the initial mass function (IMF) remain unclear. We study the CMF in the earliest stage of high-mass star formation using 461 prestellar core candidates and 254 protostellar cores as a part of the ALMA Survey of 70 µm Dark High-mass Clumps in Early Stages (ASHES). We find that prestellar core candidates tend to have lower masses than protostellar cores. We also find that the lifetime of prestellar cores is several times longer than the freefall time, although it approaches the freefall time as the core mass increases. The CMF, including both protostellar and prestellar cores, has a power-law slope of −2.05 ± 0.04, shallower than Salpeter’s IMF slope of −2.35. Conversely, the CMF of gravitationally bound, prestellar cores has a steeper slope (−2.32 ± 0.30), indistinguishable from Salpeter’s slope. This finding is consistent with observations in both low-mass star-forming regions and high-mass protoclusters, implying a universal core formation mechanism. The protostellar CMF with a larger maximum core mass can be reproduced by the prestellar CMF when an external gas infall is considered. The inferred mass infall rate is higher than the Bondi–Hoyle–Lyttleton accretion rate and follows a shallower mass dependence (smaller power-law index), more consistent with the tidal-lobe accretion. This may contribute to the evolution of CMFs seen in later stages.

We report the multiwavelength properties of eROSITA Final Equatorial Depth Survey (eFEDS) J084222.9+001000 (hereafter ID830), a quasar at z = 3.4351, identified as the most X-ray luminous radio-loud quasar in the eFEDS field. ID830 shows a rest-frame 0.5–2 keV luminosity of , with a steep X-ray photon index (Γ = 2.43 ± 0.21), and a significant radio counterpart detected with the Very Large Array FIRST 1.4 GHz and Very Large Array Sky Survey 3 GHz bands. The rest-frame UV to optical spectra from Sloan Digital Sky Survey and Subaru/MOIRCS J band show a dust-reddened quasar feature with A_V = 0.39 ± 0.08 mag, and the expected bolometric active galactic nuclei luminosity from the dust-extinction-corrected UV luminosity reaches L_bol,3000Å = (7.62 ± 0.31) × 10⁴⁶ erg s⁻¹. We estimate a black hole mass of M_BH = (4.40 ± 0.72) × 10⁸ M_⊙ based on the Mg IIλ2800 emission-line width, and Eddington ratios from the dust-extinction-corrected UV continuum luminosity and X-ray luminosity that reach λ_Edd,UV = 1.44 ± 0.24 and λ_Edd,X = 12.8 ± 3.9, respectively, both indicating super-Eddington accretion. ID830 shows a high ratio of UV to X-ray luminosities, α_OX = −1.20 ± 0.07 (or α_OX = −1.42 ± 0.07 after correcting for jet-linked X-ray excess), higher than quasars and little red dots in the super-Eddington phase with similar UV luminosities, with α_OX < −1.8. Such a high α_OX suggests the coexistence of a prominent radio jet and X-ray corona in this high-Eddington-accretion phase. We propose that ID830 may be in a transitional phase after an accretion burst, evolving from a super-Eddington to a sub-Eddington state, which could naturally describe the high α_OX.

Hybrid morphology radio sources (HyMoRSs) are a rare subclass of radio galaxies that display a Fanaroff–Riley type I (FR I) morphology on one side of the central supermassive black hole and a type II (FR II) morphology on the other. In this study, we report the discovery of 36 new HyMoRSs, marking the largest collection of such sources in the southern sky to date, using data obtained from the MeerKAT absorption line survey (MALS). The identified HyMoRSs exhibit moderate radio luminosities in the range 9.9 × 10²³–5.7 × 10²⁵ W Hz⁻¹, with a median value of 4.4 × 10²⁴ W Hz⁻¹ at 1.4 GHz, and are located within the redshift range 0.04 < z < 1.34. In this work, we show for the first time that the two lobes of HyMoRSs exhibit no statistically significant difference in their spectral indices. We also investigate the mid-infrared properties and environments of their host galaxies. Notably, 9 out of the 36 sources are situated near the centers of galaxy clusters, including one with giant radio jets that extend over 811 kpc. Our analysis reveals that the majority of HyMoRSs are hosted by actively star-forming galaxies that exhibit elevated star formation rates. Furthermore, our findings suggest that HyMoRSs may arise from FR II jets being deflected by a dense, cluster-like environment, along with orientation effects that make one jet appear FR I-like. As our candidates are selected through visual inspection of MALS radio maps, higher-resolution follow-up observations are still necessary to confirm the nature of their morphologies.

In situ observations of the fast solar wind in the inner heliosphere show that minor ions and ion subpopulations often exhibit distinct drift velocities. Both alpha particles and proton beams stream at speeds that rarely exceed the local Alfvén speed relative to the core protons, suggesting the presence of instabilities that constrain their maximum drift. We aim to propose a mechanism that generates an alpha-particle beam through nonlinear Landau damping, primarily driven by the relative super-Alfvénic drift between protons and alpha particles. To investigate this process, we perform one-dimensional, fully kinetic particle-in-cell simulations of a nonequilibrium multispecies plasma complemented by its linear theory to validate the model during the linear phase. Our results provide clear evidence that the system evolves by producing an alpha-particle beam, thereby suggesting a local mechanism for alpha-beam generation via nonlinear Landau damping.

Magnetohydrodynamic (MHD) simulations are a useful tool for understanding the propagation of coronal mass ejections (CMEs) in the inner heliosphere and their interaction with the background solar wind. This understanding is important for improving our ability to predict CME properties at Earth. A common approach in models of the inner heliosphere starting from ≈0.1 astronomical unit (au) is to inject CMEs with analytically prescribed magnetic structures—such as magnetic spheromaks—by superimposing the CME’s magnetic field onto the heliospheric magnetic field. However, the superposition method leads to the heliospheric magnetic field penetrating the CME, immediately distorting the CME’s magnetic structure during the injection. In this work, we introduce a new, more physically accurate displacement method for the CME injection into the inner heliosphere by dynamically bending the heliospheric magnetic field around the incoming CME. Using the GAMERA-Helio MHD model of the inner heliosphere (0.1–1 au) and a Gibson–Low model of a CME with an internal magnetic field, we demonstrate that the displacement method preserves the CME’s internal structure, unlike superposition. Moreover, the displacement method produces a current distribution around the CME that is consistent with results from previous coronal MHD simulations with a self-consistent description of CME initiation and evolution. The displacement approach represents a step forward in modeling magnetized CMEs in the inner heliosphere to study their evolution and impacts at Earth.

Type II orbital migration is a key process to regulate the mass and semimajor axis distribution of exoplanetary giant planets. The conventional formula of Type II migration generally predicts too rapid inward migration to reconcile with the observed pileup of gas giants beyond 1 au. Analyzing the recent high-resolution hydrodynamical simulations by Y.-P. Li et al. and J.-P. Pan et al. that show robust outward migration of a gas accreting planet, we here clarify the condition for the outward migration to occur and derive a general semianalytical formula that can be applied for a broad range of planet mass and disk conditions. The striking outward migration is caused by azimuthal asymmetry in corotation torque exerted from circumplanetary disk regions (connecting to horseshoe flows) that is produced by the planetary gas accretion, while the conventional inward migration model is based on radial asymmetry in the torques from the circumstellar protoplanetary disk. We found that the azimuthal asymmetry dominates and the migration is outward when the gap depth defined by the surface density reduction factor of is in the range of . Using simple models with the new formula, we demonstrate that the outward migration plays an important role in shaping the mass and semimajor axis distribution of gas giants. The concurrent dependence of planets’ accretion rate and migration direction on their masses and disk properties potentially reproduces the observed pileup of exoplanetary gas giants beyond 1 au, although more detailed planet population synthesis calculations are needed in the future.

Migration typically occurs during the formation of planets and is closely linked to the planetary formation process. In classical theories of nonaccreting planetary migration, both type I and type II migration typically result in inward migration, which is hard to align with the architecture of planetary systems. In this work, we conduct systematic, high-resolution 3D/2D numerical hydrodynamic simulations to investigate the migration of an accreting planet. Under different disk conditions, we compared the dynamical evolution of planets with different planet-to-star mass ratios. We find that accretion of planets can significantly diminish the inward migration tendency of planets, or even change the direction of migration. The migration of low-/high-mass planets is classified as type I/II inward migration, respectively, while intermediate-mass planets, which have the strongest accretion, show an outward migration trend. We confirm that the outward migration is mainly attributed to the positive torque from the azimuthal asymmetric structures around the accreting planet, similar to Y.-P. Li et al. The termination of planetary mass growth is thus synonymous with the transition from outward to inward migration. For the cases of high viscosity α = 0.04 and disk aspect ratio h₀ = 0.05, the range of mass ratio for planetary outward migration is 1 × 10⁻⁴ ≲ q ≲ 4 × 10⁻³. For the case of low viscosity with α = 0.001 and/or low disk aspect ratio h₀ = 0.03, the range of mass ratio for outward migration will shift toward the lower end. Our parameter survey reveals that a simple gap-opening parameter determines the condition for outward migration; details of the analytical interpretation are presented by S. Ida et al.

Supersoft X-ray sources (SSSs) are characterized by persistent thermonuclear burning on the surfaces of white dwarfs (WDs). The standard model requires high mass-transfer rates of ∼10⁻⁷M_⊙ yr⁻¹ from massive companions, presenting a theoretical impediment to the observed short-period SSSs, whose orbital periods imply low-mass donors theoretically incapable of sustaining such accretion. To resolve this paradox, we propose and demonstrate through detailed simulations that irradiative feedback following a classical nova eruption provides a natural formation channel. Through detailed binary evolution simulations with MESA, we reveal that sustained WD irradiation—initially from the outburst and subsequently from accretion luminosity—triggers significant and stable expansion of the low-mass companion. This, in turn, drives mass-transfer rates into the stable hydrogen-burning regime and sustains it beyond 10⁴ yr after the initiation of hydrogen burning. This mechanism robustly explains the observed population of short-period SSSs. Moreover, when the irradiation-driven mass-transfer rate drops below the stable accretion rate, it may lead to the rapid accumulation of sufficient material on shorter timescales to trigger a recurrent nova outburst instead of SSS, thereby also offering an explanation for the origin of short-period recurrent novae.

“PeVatrons” refer to astrophysical sources capable of accelerating particles to energies of ∼PeV and higher, potentially contributing to the cosmic-ray spectrum in the knee region. Recently, the High-Altitude Water Cherenkov Observatory (HAWC) and the Large High Altitude Air Shower Observatory (LHAASO) have discovered a new type of PeVatron–X-ray binary, allowing us to investigate in greater depth the contributions of these sources to cosmic rays around the knee region. There are hundreds of X-ray binaries observed in our Galaxy that are potential PeVatrons. In this work, we derive the radial distribution of X-ray binaries in the Galaxy. Then we use the DRAGON package to calculate energy spectrum, anisotropy of cosmic rays, and the resulting diffuse gamma-ray emissions, after considering them as factories of cosmic rays in the knee energy bands. Our findings show that the contributions from X-ray binary PeVatrons may be dominant. More X-ray binary PeVatrons can be observed by LHAASO and HAWC in the future and will confirm the contribution of X-ray binaries to high-energy cosmic rays.

Radio emission from pulsars is known to exhibit a diverse range of emission phenomena, among which nulling, where the emission becomes temporarily undetectable, is an intriguing example. Observations suggest nulling is prevalent in many long-period pulsars and thus must be understood to obtain a more comprehensive picture of pulsar emission and its evolution. However, one of the limitations in the observational characterization of nulling is the limited signal-to-noise ratio, which often makes individual pulses difficult to distinguish from noise or from any putative faint emission. Although some of the approaches in the published literature attempt to address this, they lose efficacy when individual pulses appear indistinguishable from noise, and as a result can lead to less accurate measurements. Here, we develop a new method (the sum algorithm) that uses sums of pulses to improve distinguishability from noise, thus measuring the nulling fraction more robustly. The algorithm can be employed to measure nulling fractions in weaker pulsars and can be applied to observations with a limited number of pulses. We compare our method with the recently developed Gaussian mixture modeling approach, using both simulated and real data, and find that our approach yields consistent results for generic and weaker pulsars. We also explore quasiperiodicity in nulling and measure the related parameters for five pulsars, including PSRs J1453−6413, J0950+0755, and J0026−1955, for which these are also the first such measurements. We compare and contrast our analysis of quasiperiodic nulling with previously published work, and explore the use of spin-down energy loss () to distinguish between different types of modulation behaviour.

Massive stars (>8 M_⊙) often undergo intense mass loss through winds or eruptive events in the final stages of their evolution, leading to the formation of a dense circumstellar medium (CSM). This material, expelled months to years before core collapse, shapes the pre-explosion environment and influences the early supernova (SN) emission. In particular, the interaction of the SN ejecta with the dense CSM can power an extended emission into the ultraviolet(UV)/optical bands, as seen in a growing fraction of type II SN. Recent events such as SN 2023ixf and SN 2024ggi confirm the relevance of dense environments and highlight the value of UV observations. Moreover, fast blue optical transients may represent extreme cases of this interaction, possibly linked to more compact/massive CSM. In this work, we model the SN–CSM shock interaction in order to (i) estimate the maximum detection horizons and expected rates for future UV missions like ULTRASAT, and (ii) to estimate the intensity and expected rate of potential neutrino signals detectable by IceCube and KM3NeT. We then discuss the prospects for multi-messenger observations of such events in the near future.

We present X-ray observations of the periodic optical source ZTF J185139.81+171430.3 (hereafter ZTF J1851) by the XMM-Newton, NICER, and NuSTAR telescopes. The source was initially speculated to be a white dwarf (WD) pulsar system, due to its short period (P ∼ 12 minutes) and highly modulated optical lightcurves. Our observations revealed a variable X-ray counterpart extending up to 40 keV with an X-ray luminosity of L_X ∼ 3 × 10³³ erg s⁻¹ (0.3–40 keV). Utilizing timing data from XMM-Newton and NICER, we detected a periodic signal at P_spin = 12.2640(7) ± 0.0583 minutes with >6σ significance. The pulsed profile displays ∼25% and ∼10% modulation in the 0.3–2 and 2–10 keV bands, respectively. Broadband X-ray spectra are best characterized by an absorbed optically thin thermal plasma model with kT ≈ 25 keV and a Fe K-α fluorescent line at 6.4 keV. The bright and hard X-ray emission rules out the possibility of a WD pulsar or ultra-compact X-ray binary. The high plasma temperature and Fe emission lines suggest that ZTF J1851 is an intermediate polar spinning at 12.264 minutes. We employed an X-ray spectral model composed of the accretion column emission and X-ray reflection to fit the broadband X-ray spectra. Assuming spin equilibrium between the WD and the inner accretion disk, we derived a WD mass range of M_WD = (1.07–1.32)M_⊙, exceeding the mean WD mass of IPs (〈M_WD〉 = 0.8M_⊙). Our findings illustrate that follow-up broadband X-ray observations could provide unique diagnostics to elucidate the nature of periodic optical sources anticipated to be detected in the upcoming Rubin all-sky optical surveys.

The irradiance received by a spherical body or a planet close to a spherically symmetric source does not follow the point-source approximation and the inverse-square variation of irradiation if spherical symmetry is broken. In the penumbral zones of the planet, spherical symmetry of the star reduces to an axial symmetry. Our work aims to put forward a fundamental explanation, using energy conservation, to determine the variation of irradiance in the penumbral zone on a close-in planet where the point-source approximation fails. Consequently, we propose a numerical model that accurately predicts the irradiance within the boundaries of the penumbral zone and the fully illuminated zone. Our analysis also corrects a previous study on exoplanet irradiation that violates energy conservation. We find that night-side illumination partially explains the observed night-side temperatures on the planets considered; this reduces reliance on heat transport models to explain the night-side temperature for the few exemplar rocky close-in planets, namely K2-141 b, 55 Cancri e, TOI-561 b, TOI-431 b, and Kepler-10 b, that are discussed in this work. We provide improved day–night contrast temperatures, considering an airless scenario, and highlight the need for revisiting the heat transport models associated with atmospheric modelling of planets where the night-side illumination is significant.

We present an analysis of the radio quiescent data from a multiwavelength campaign of the active M dwarf flare star AU Mic (dM1e) that occurred in 2018 October. Using Ku-band data (12–18 GHz) from the Karl G. Jansky Very Large Array and K-band data (17–25 GHz) from the Australia Telescope Compact Array, we find that the quiescent spectrum can be decomposed into two components: one falling with frequency and one that remains flat. The flat component has a relatively steady flux density of 0.64 ± 0.14 mJy. The falling component varies in strength, but exhibits a spectral index of α = −0.88 ± 0.10. The falling component is thus consistent with nonthermal, optically thin gyrosynchrotron radiation with a corresponding power-law index similar to flares from AU Mic. While a flat component may arise from thermal, optically thin free–free emission, the observed flux density and inferred mass-loss rate are both too large compared to previous stellar wind and X-ray emission theory and models, necessitating an alternative explanation. This flat component instead matches well with an optically thick gyroresonance component integrated over multiple source regions such that the composite spectra are reasonably flat. The persistence of these components across the rotational period suggests multiple source regions, which may help explain changes in flux density and persistent high-energy electrons.

Von Zeipel–Lidov−Kozai (ZLK) oscillations, induced by bound, perturbative companions to white dwarfs (WDs), have been suggested as a dynamical mechanism that may contribute to WD pollution. To trigger ZLK oscillations, however, a three-body system must reach a sufficiently large mutual inclination between orbits. The occurrence of these high-mutual-inclination configurations can be curtailed by dissipative precession at the protoplanetary disk stage, which pushes exoplanet-hosting close binary systems toward preferential orbit–orbit alignment. In this work, we constrain the fraction of WDs with binary companions that can undergo ZLK-driven pollution given the effects of dissipative precession. To accrete pollution via ZLK oscillations, a WD binary system must be sufficiently inclined and the characteristic timescale of the oscillations must be sufficiently short to perturb material within the WD’s cooling age. Considering a sample of 4400 known WD/main-sequence binaries, we find that 50%–70% have favorable parameters for ZLK pollution, depending on the orbital separation of the polluting body. While the conditions for oscillations are favorable, the tendency for ZLK to result in massive but more infrequent polluters likely restricts the rates of ZLK-induced pollution among the observed population. In general, dissipative precession is a limiting factor in pollution rates for more closely separated binaries (initial separations <500−800 au), while ZLK timescale constraints are most limiting for wider binaries.

Spicules are among the most ubiquitous small-scale, jet-like features in the solar chromosphere and are widely believed to play a significant role in transporting mass and energy into the solar corona, with their mechanisms not fully understood. We utilize high-resolution Hα images acquired from the 1.6 m Goode Solar Telescope at Big Bear Solar Observatory to investigate spatial and dynamical properties of both spicules and network bright points (NBPs), and for the first time, incorporated NBP motions in the analyses of spicules. Our main results are as follows: (1) The speed distributions of blueshifted spicules and NBPs both exhibit distinct peaks, whereas that of redshifted spicules is monotonically decreasing. (2) Torsional motions of spicules inferred from alternating signs of Doppler shifts are faster than the NBPs’ transversal motions by a factor of 10–10², which may imply the mass density ratio in two different heights as 10²–10⁴. (3) Blueshifted spicules are found to be more abundant than redshifted spicules in general, but their relative population difference reduces to ∼10% at Doppler speeds above ∼35 km s⁻¹. (4) Redshifted spicules lying at higher heights share morphological and dynamical similarity with the blueshifted spicules, which implies the same driving mechanism operating in both directions. (5) These two populations appear above NBPs concentrated under the AIA 193 Å bright region. We interpret these results in favor of a scenario that Alfvén waves generated by NBPs' motions impart their energies to spicules in both torsional and field-aligned motions, and also contribute to the coronal heating and possibly the acceleration of the solar wind.

We present narrowband observations of the Fe xiv (530.3 nm), Fe x (637.4 nm), and Fe xi (789.2 nm) coronal emission lines from the 2023 April 20 Total Solar Eclipse in Australia. We deployed pairs of telescopes for each emission line that were equipped with narrowband filters centered on, and several nanometers away from, the center wavelengths of the lines. The secondary continuum telescopes were used to measure and remove the combined continuum K- (electron) and F- (dust) corona, which dominate coronal emission at optical and infrared wavelengths. Significant emission was detected from all three lines from 1.03 solar radii (R_⊙) continuously outward to at least 6 R_⊙. The brightness of the lines and continuum are absolutely calibrated to the solar disk, and are validated by a comparison with LASCO-C2 observations made at the same time. Using these observations, we inferred the line emission ratios resolved throughout the middle-corona (defined as 1.5–6 R_⊙) for the first time. These line ratios are a probe of the electron temperature, which have important implications for constraining models of coronal heating and the characterization of solar wind formation, yet these emission lines have scarcely been quantified beyond 3 R_⊙ in the corona. This study demonstrates the enduring potential of eclipse observations for coronal physics and suggests that future spacecraft missions could observe these lines farther out than has been attempted previously.

The recent detections of radio emission from the nearby exoplanet host, YZ Ceti, suggest that the star is possibly interacting with its rocky innermost planet. These radio emissions are characterized by strong circular polarization, and appear to repeat within consistent orbital phase windows dictated by the orbital position of YZ Ceti b. If confirmed, this interaction would provide a first means to concretely assess the magnetic field of a close-in rocky exoplanet. This kind of magnetic star–planet interaction (SPI) should depend on both the exoplanetary orbit and the geometry of the stellar magnetic field. In this article, we report measurements of the large-scale magnetic field topology of the star YZ Ceti for the first time, and interpret the cumulative radio data sets in that context to evaluate the plausibility of magnetic SPIs. We find evidence both against and in support of the SPI hypothesis, but crucially that the measured magnetic field does not rule out SPI scenarios. However, clear evaluation of these possibilities requires more accurate assessments of the magnetic field evolution across time. We additionally suggest that YZ Ceti may be exhibiting planet-induced flaring, potentially triggered by exoplanet crossings of the Alfvén surface as the planet’s orbit approaches the stellar magnetic equator, and YZ Ceti b experiences dramatic shifts in the ambient field, its polarity, and connectivity to the host star.

A newly born millisecond magnetar has been proposed as one possible central engine of some long gamma-ray bursts (LGRBs) with X-ray plateau emission. In this work, we used a universal correlation between the initial spin period (P₀) and the surface magnetic field (B_p) of the newborn magnetar based on an LGRB sample in L. Lan et al. (2025) to explore the propeller properties of accreting magnetars with R/I evolutionary effects. We found that the B_p–P₀ relation is approximately consistent with . Here P_eq is the equilibrium spin period in the magnetic propeller model, where the electromagnetic dipole radiation and the propeller mechanism jointly modulate the spin evolution of a newborn magnetar. The B_p–P₀ relation indicates that P₀ constrained by X-ray plateau data may not be the true initial spin period of a newborn magnetar but had reached an equilibrium spin period via fallback accretion in the propeller model. The magnetar accretion rate in our LGRBs is in the range of by incorporating R/I evolutionary effects and using the transition relation between gravitational mass M_g and baryonic mass M_b in different equations of state and X-ray radiation efficiencies. Such accretion rates ensure that the accreting magnetars in our sample survive until reaching the equilibrium spin period, and the accretion rate is one order of magnitude lower compared to the statistical results in G. Stratta et al. (2018) and W. L. Lin et al. (2020), which used the constant R/I/M_g scenario. The fallback rate of progenitor envelope materials onto the magnetar accretion disk for our LGRBs is compatible with the theoretical mass fallback rate of some low-metallicity progenitors. We suggested that adopting a constant R/I/M_g scenario for modeling the propeller regime in accreting magnetars results in a higher mass accretion rate, which may impair our understanding of the physical nature of an accreting magnetar and its surroundings, and that the low-metallicity progenitors can provide enough material to satisfy the accretion requirements of the newborn accreting magnetar in LGRBs.

The heliospheric current sheet (HCS) is an important large-scale structure of the heliosphere, and, for the first time, the Parker Solar Probe (PSP) mission enables us to study its properties statistically, close to the Sun. We visually identify the 39 HCS crossings measured by PSP below 50 R_⊙ during encounters 6–21, and investigate the occurrence and properties of magnetic reconnection, the behavior of the spectral properties of the turbulent energy cascade, and the occurrence of kinetic instabilities at the HCS. We find that 82% of the HCS crossings present signatures of reconnection jets, showing that the HCS is continuously reconnecting close to the Sun. The proportion of inward and outward jets depends on heliocentric distance, and the main HCS reconnection X-line has a higher probability of being located close to the Alfvén surface. We also observe a radial asymmetry in jet acceleration, where inward jets do not reach the local Alfvén speed, contrary to outward jets. We find that turbulence levels are enhanced in the ion kinetic range, consistent with the triggering of an inverse cascade by magnetic reconnection. Finally, we highlight the ubiquity of magnetic hole trains in the high-β environment of the HCS, showing that the mirror mode instability plays a key role in regulating the ion temperature anisotropy in HCS reconnection. Our findings shed new light on the properties of magnetic reconnection in the high-β plasma environment of the HCS, its interplay with the turbulent cascade, and the role of the mirror mode instability.

We investigate magnetic field amplification driven by the nonresonant hybrid (NRH, or Bell) instability and its impact on cosmic-ray (CR) acceleration at the reverse shocks of ultrafast outflows (UFOs) from active galactic nuclei. Previous kinetic studies by particle-in-cell simulations have demonstrated that when the maximum CR energy is near the injection scale, the NRH instability efficiently amplifies the magnetic field up to the saturation level. However, the efficiency of the NRH instability decreases as the maximum energy increases, since the CR current is carried by escaping CRs near the maximum energy. We employ a one-dimensional MHD-CR framework solving telegraph-type diffusion–convection equations to trace the coupled evolution of CRs, magnetic fields, and shock dynamics under realistic parameters. We find a distinct transition with magnetic field strength. For weak background fields (B₀ ≲ 10⁻⁴ G), the NRH instability efficiently amplifies upstream turbulence, driving a self-regulated state where becomes independent of the initial strength of the magnetic turbulence. In contrast, for stronger background fields (B₀  ≳ 10⁻³ G), the escaping CR current is too weak to drive the NRH instability, and magnetic turbulence further decays through parametric instabilities, potentially reducing the acceleration efficiency. We give a physical interpretation for the transition and discuss conditions for PeV to EeV acceleration at UFO reverse shocks.

We present a comprehensive analysis of the 150 MHz radio luminosity function (LF) of star-forming galaxies (SFGs) using deep observations from the LOFAR Two-metre Sky Survey in the ELAIS-N1, Boötes, and Lockman Hole fields. Our sample comprises ∼56,000 SFGs over 0 < z < 5.7. We first analyze the deepest field (ELAIS-N1), then jointly model all three fields while accounting for their distinct flux limits and selection functions. Using adaptive kernel density estimation (KDE), we reconstruct the LF continuously across redshift and luminosity without binning or parametric assumptions. The KDE results reveal clear signatures of joint luminosity and density evolution (LADE). Motivated by this, we construct and fit three parametric models—pure luminosity evolution (PLE) and two LADE variants—using a full maximum-likelihood method that includes completeness corrections and constraints from the local radio LF and Euclidean-normalized source counts (SCs). Model selection using Akaike and Bayesian information criteria strongly favors LADE over PLE. For ELAIS-N1, the more flexible LADE model (Model C) provides the best fit, while for the combined fields, the simpler Model B balances fit quality and complexity more effectively. Both LADE models reproduce the observed LFs and SCs across luminosity and flux density ranges, whereas PLE underperforms. We also identify a mild excess at the bright end of the LF, likely due to residual active galactic nucleus contamination. This study demonstrates that combining KDE with parametric modeling offers a robust framework for quantifying the evolving radio LF of SFGs, paving the way for future work with next-generation surveys like the Square Kilometre Array.

We present a comprehensive analysis of 475 ks (438 ks unpublished and 37 ks archival) XMM-Newton/EPIC-pn observations of a nearby, highly inclined, star-forming, luminous infrared galaxy NGC 3221 through spatial, temporal, and spectral information. We confirm the presence of a low-luminosity (presumably Compton-thick) active galactic nucleus (AGN). The 0.4–12 keV luminosity and the hardness ratio of the six ultraluminous X-ray sources previously identified in Chandra data exhibit diverse variability on day scales. The collective emission from unresolved sources exhibits a different day-scale variability. We have also discovered two new predominantly soft (<1 keV) sources. One of these has an enigmatic spectral shape featuring a soft component, which we interpret as a superbubble in NGC 3221, and a variable hard component from a compact object, unresolved from the superbubble. We do not confidently detect any X-ray emission from SN 1961L. The hot gas in the interstellar medium (ISM, out to ±6 kpc from the disk plane) and that in the extraplanar region (6–12 kpc) both require two thermal phases at ∼0.15 keV and ∼0.55 keV. The ∼0.55 keV component is fainter in the ISM than the ∼0.15 keV component, but the emission from the latter falls off more steeply with disk height than the emission from the former. This makes the extraplanar region hotter and less dense than the ISM. The proximity of NGC 3221 and the occurrence of the underluminous AGN offer a unique observing opportunity to study the hot diffuse medium along with nuclear and diskwide point sources.

The nature of MHD waves within inhomogeneous media is fundamental to understanding and interpreting wave behavior in the solar atmosphere. We investigate fast magnetoacoustic wave behavior within gravitationally stratified, magnetically inhomogeneous media, by studying a magnetic environment containing a simple 2D X-type magnetic null point. The addition of gravitational stratification fundamentally changes the nature of the system, including breaking the symmetry. There are two main governing effects: the stratified density profile acts in combination with the inhomogeneous magnetic field, creating a large gradient in the Alfvén speed and hence a system replete with refraction. The system is investigated using both numerical simulations and a semianalytical WKB solution (via Charpit’s method and a fourth-order Runge–Kutta solver) and we find strong agreement between both. The results show a fundamental difference between the stratification-free and stratified cases, including the formation of caustic surfaces and cusps, and we contextualize these results in the theoretical understanding of fast magnetoacoustic waves.

We present and analyze panchromatic (0.35–14 μm) spectroscopy of the Type II supernova 2023ixf, including near- and mid-infrared spectra obtained 33.6 days after explosion during the plateau phase, with the James Webb Space Telescope (JWST). This is the first in a series of papers examining the evolution of SN 2023ixf with JWST during the initial 1000 days after explosion and monitoring the formation and growth of molecules and dust in ejecta and the surrounding environment. The JWST infrared spectra are overwhelmingly dominated by H lines, whose profiles reveal ejecta structures, including flat tops, blue notches, and red shoulders, unseen in the optical spectra. We characterize the nature of these structures, concluding that they likely result from a combination of ejecta geometry, viewing angle, and opacity effects. We find no evidence for the formation of dust precursor molecules such as carbon monoxide (CO), nor do we observe an infrared excess attributable to dust. These observations imply that the detections of molecules and dust in SN 2023ixf at later epochs arise either from freshly synthesized material within the ejecta or circumstellar material at radii not yet heated by the supernova at this epoch.

The properties of the population of compact objects created in core-collapse supernovae (SNe) are uncertain. X-ray observations years to decades after the explosions offer a way to gain insight into this, as hard X-ray emission from the central regions will emerge as the ejecta absorption decreases. Here, we analyze and place upper limits on late-time X-ray emission in 242 nearby SNe, using 607 observations from Chandra, XMM-Newton, Swift, and NuSTAR. We use absorption models based on 3D simulations of neutrino-driven explosions to account for absorption of emission from the compact objects by the asymmetric ejecta. We detect X-ray emission from 12 SNe, including 4 for the first time (SN 1982R, SN 1984J, SN 1992bu, and SN 2003gk), and several of the others at later epochs than before. The X-ray spectra of these SNe are consistent with interaction with the circumstellar medium (CSM), with the possible exception of SN 1979C, which shows an additional hard component, as also noted in previous studies at earlier epochs. This emission may be due to a pulsar wind nebula. Using the upper limits in the full sample, we also perform a population synthesis to constrain the fraction of SNe that produce pulsars and the properties of the pulsars themselves. We find that pulsar populations with mean initial spin periods ≳100 ms are favored. Finally, we note that the high luminosities of several of the SNe with CSM interaction imply interactions with dense shells.

It is widely believed that the ultraviolet background produced during the epoch of reionization conspires against the formation of low-mass galaxies. Indeed, this mechanism is often invoked as part of the solution to the so-called “missing satellites problem.” In this paper we employ FIREbox, a large-volume cosmological simulation based on the Feedback In Realistic Environments physics model, to characterize the mechanisms governing galaxy ignition in the postreionization era. By carefully matching recently ignited halos (with stellar ages below 100 Myr at the time of selection) to halos that failed to form any stars, we conclude that the presence of cold dense gas and halo concentration helps incite the process of galaxy formation. Concretely, we find that 100% of recently ignited halos experience cold dense gas enhancements relative to their matched failed counterparts. Likewise, approximately 83% display enhancements in both cold dense gas and Navarro–Frenk–White concentration (c_NFW), while the remaining ∼17% exhibit enhanced cold dense gas content and suppressed c_NFW values. Lastly, our simulation suggests that galaxy ignition can occur as late as z = 2, potentially allowing us to observationally catch this process “in the act” in the foreseeable future.

Next-generation surveys are expected to uncover thousands of globular cluster (GC) stellar streams, motivating the need for a theoretical framework that produces realistic GC streams in a fully cosmological, Milky Way–like environment. We present CosmoGEMS, a star-by-star cosmological GC stream framework that self-consistently links small-scale cluster physics with large-scale Galactic dynamics. The initial phase-space positions of stream stars are informed by post-processed GC populations within the FIRE cosmological simulation. Escaped stars are orbit-integrated from their time of escape to the present day in a time-evolving Galactic potential extracted from the same simulation using a basis function expansion. We explore two example streams on different orbits. One forms a long, thin stream with a velocity dispersion consistent with Milky Way GC streams. However, it exhibits a clump and orbital-phase-dependent misalignments due to the evolving potential. The other stream develops both a thin component and a diffuse, shell-like structure, similar to features observed in streams like Jhelum. These results highlight the power of fully cosmological models in producing realistic stream morphologies and kinematics. Unlike idealized simulations, our models naturally incorporate time-dependent changes in the progenitor’s orbit, including orbital plane evolution, which significantly affects stream structure. This challenges common assumptions in stream-finding algorithms and interpretation. CosmoGEMS provides a key step toward connecting future stellar stream observations with the physics of GC evolution and hierarchical galaxy formation in a cosmological context.

The inner circumgalactic medium (CGM) of galaxies, where disk and halo processes intersect, remains poorly characterized despite its critical role in regulating galaxy evolution. We present results from Project AMIGA Insider, mapping Andromeda’s (M31) inner CGM within 0.25 R_vir (∼75 kpc) using 11 QSO sightlines, bringing our total sample to 54 sightlines from the disk to 2R_vir. We detect a clear transition between M31’s thick disk and CGM at R ≲ 30 kpc, where low/intermediate ions show thick-disk corotating components with higher column densities than the CGM ones, while high ions exhibit similar column densities in both the CGM and thick disk. Beyond this region, all ion column densities decrease with impact parameter, with steeper gradients for low ions than high ions. The inner CGM (R ≲ 100 kpc) shows more complex gas phases and multicomponent absorption compared to the predominantly single-component outer CGM. We find no significant azimuthal dependence for any observed ions, suggesting M31’s CGM is shaped by radial processes (e.g., cooling flows, precipitation) rather than disk-aligned outflows. We estimate the total metal mass in M31’s cool (Si ii, Si iii, Si iv) CGM within R_vir to be (1.9 ± 0. 3_stat ± 0. 7_sys) × 10⁷M_⊙, leading to a cool gas mass of M_⊙. The warmer O vi gas may contain at least 10 times more metal and gas mass. Compared to the COS-Halos L*galaxies, M31’s cool CGM shows lower Si column densities at R ≲ 0.4 R₂₀₀ and overall lower cool CGM masses, likely reflecting differences in galaxy mass and environment.

High-energy blazar light curves, in X-rays and beyond, have historically preferred a log-normal flux distribution, signifying multiplicative processes either in the jet itself or due to connection(s) with accretion. Here we present 18 yr archival Fermi Large Area Telescope light curves (0.1–100 GeV) of the flat spectrum radio quasar CTA 102 from 2008 August to 2025 November, which underwent a huge flare in 2017, with a ∼ factor of 100 jump in γ-ray flux, along with similar flaring in X-rays. Our statistical analyses confirm that neither the pre- nor the postflare total GeV light curves follow a strictly log-normal distribution. Instead, we observe a statistically significant reduction in skewness from the pre- to the postflare light curves, which implies the blazar transitioned from an energetic state with frequent flaring to a more plateaued state with occasional flaring. We further find that this state transition can be explained through magnetic relaxation, where many reconnection events caused the 2017 flare, after which the magnetic field was ordered and its energy reached a minimum. To explain this further, we use a Monte Carlo simulation of a modified minijets-in-a-jet model where GeV flares are produced only when a maximum number of minijets move toward the broad line region and toward the line of sight, in the context of an external Compton model. The flux distributions (both observed and simulated) could be fit by a modified log-normal power-law distribution, implying our minijets model can reproduce the GeV flares in CTA 102 as well as their flux distributions.

Observing giant H II regions at fine spatial scales uncovers detailed structures and reveals variations in ionization, abundance, and dynamical properties of ionized gas and the effect of stellar feedback. Using emission-line data of M33 observed with SITELLE as part of the Star-formation, Ionized Gas, and Nebular Abundances Legacy Survey (SIGNALS), we present maps of the principal optical emission-line ratios for NGC 604, the most luminous H ii region in M33. The excitation maps align well with the Hα morphology and are clearly related to the location of the central stellar cluster and secondary stellar groups. The maps of ionization-sensitive line ratios show substantial variations across the face of NGC 604. We demonstrate that these variations are unlikely to be due to chemical inhomogeneities but are primarily caused by changes in ionization, which in turn affect the observed line ratios. We present the Hα kinematics of the region and connect it to the excitation structure, showing how the dynamic motions influence the spatial distribution of ionized gas. We note two distinct sources identified in these excitation maps: a known supernova remnant and a previously unknown planetary nebula. Such parsec-scale features contribute only a small percentage to the overall light and would remain undetected without the use of high-resolution spatial data. Throughout the paper, we make comparisons to and raise concerns about single-aperture and long-slit spectroscopic measurements of giant H II regions, highlighting the limitations and potential inaccuracies of such methods.

AT 2020vdq has been known as a candidate of repeating partial tidal disruption events (pTDEs) due to its two flares with a time interval of ∼1000 days. Here, a simplified method is proposed to test such repeating pTDEs scenario considering a main-sequence star tidally disrupted twice. For the two flares in AT 2020vdq if related to the repeating pTDEs scenario, a theoretical tidal disruption event (TDE)–model determined stellar mass of the original star disrupted for the first flare should be not very different from the mass of the star (to trace the reminder of the original star) disrupted for the second flare because a pTDE with impact parameter β smaller than 1 can lead to most of (probable higher than 90%) the stellar mass also bound to the reminder of the original star. After considering theoretical TDE model applied to describe the two flares in AT 2020vdq, the model determined stellar masses are about 2 and 0.36 M_⊙ for the stars disrupted in the first flare and the second flare. The large mass difference cannot be reasonably expected by the repeating pTDEs with β around 0.6 in AT 2020vdq. The results in this manuscript indicate that the repeating pTDEs scenario is not preferred at current stage in AT 2020vdq, but the probable double TDEs for two individual stars tidally disrupted should be currently recommended.

From the luminous quasars at z ∼ 6 to the recent z ∼ 9–11 active galactic nuclei (AGN) revealed by JWST, observations of the earliest black hole (BH) populations can provide unique constraints on BH evolution. We use the BRAHMA simulations with constrained initial conditions to investigate BH assembly in extreme overdense regions. The simulations implement heavy ∼10⁴–10⁵ M_⊙ seeds forming in dense, metal-poor gas exposed to sufficient Lyman–Werner flux. With gas accretion modeled via the Bondi–Hoyle formalism and BH dynamics with a subgrid dynamical friction scheme, we isolate the impact of seeding, dynamics, accretion, and feedback on BH evolution. With fiducial stellar and AGN feedback inherited from IllustrisTNG, accretion is suppressed at z ≳ 9, leaving mergers as the dominant growth channel. Gas accretion dominates at z ≲ 9, where permissive models (super-Eddington or low radiative efficiency) build ∼10⁹ M_⊙ BHs powering quasars by z ∼ 6, while stricter IllustrisTNG-based prescriptions yield much smaller BHs (∼10⁶–10⁸ M_⊙). Our seed models strongly affect mergers at z ≳ 9: only the most lenient models (with ∼10⁵ M_⊙ seeds) produce enough BH mergers to reach ≳10⁶ M_⊙ by z ∼ 10, consistent with current estimates for GN-z11. Our dynamical friction model gives low merger efficiencies. Therefore, even in such extreme regions, we are unable to produce ≳10⁷ M_⊙ BHs by z ∼ 9–10, as currently inferred for GHZ9, UHZ1, and CAPERS-LRD-z9. If the BH-to-stellar mass ratios of these sources are indeed so extreme, they would require either very short BH merger timescales or reduced AGN thermal feedback. Weaker stellar feedback boosts both star formation and BH accretion and cannot raise these ratios.

We test the impact of an evolving supermassive black hole mass scaling relation (M_BH–M_bulge) on the predictions for the gravitational-wave background (GWB). The observed GWB amplitude is 2–3 times higher than predicted by astrophysically informed models, which suggests the need to revise the assumptions in those models. We compare a semi-analytic model’s ability to reproduce the observed GWB spectrum with a static versus evolving-amplitude M_BH–M_bulge relation. We additionally consider the influence of the choice of galaxy stellar mass function (GSMF) on the modeled GWB spectra. Our models are able to reproduce the GWB amplitude with either a large number density of massive galaxies or a positively evolving M_BH–M_bulge amplitude (i.e., the M_BH/M_bulge ratio was higher in the past). If we assume that the M_BH–M_bulge amplitude does not evolve, our models require a GSMF that implies an undetected population of massive galaxies (M_⋆ ≥ 10¹¹M_⊙ at z > 1). When the M_BH–M_bulge amplitude is allowed to evolve, we can model the GWB spectrum with all fiducial values and an M_BH–M_bulge amplitude that evolves as α(z) = α₀(1 + z)^1.04±0.5.

We report the spectroscopic detection of neutral gas inflow into a massive (M_* ≃ 4 × 10¹⁰ M_⊙) quiescent galaxy observed at z_spec = 2.6576 with the James Webb Space Telescope (JWST). From the redshifted absorption of the Na I doublet at λλ5890, 5896, we estimate an inflow velocity km s⁻¹ and a column density . We derive the inflowing mass of the gas and rate . The presence of several surrounding galaxies suggests that the galaxy may be accreting gas from nearby companions. However, we cannot confirm this with current data, and the intergalactic medium or cosmic filaments are also viable sources of the inflowing gas. Despite the ongoing inflow, the galaxy remains quiescent, with an upper limit to the star formation rate of 0.2 M_⊙ yr⁻¹. Moreover, its star formation history suggests that the galaxy has remained quiescent during the past ∼1 Gyr, with half of its stars formed by redshift . We discuss that the inflow is not massive, dense, or long-lived enough to ignite significant star formation (SF), or it is fueling low-level active galactic nucleus activity instead. This is direct evidence that quiescent galaxies can accrete cold gas after their quenching while keeping their SF subdued. Follow-up observations with JWST and the Atacama Large Millimeter/submillimeter Array will be needed to constraint the nature of the inflowing gas.

Shocks driven by coronal mass ejections (CMEs) are the most powerful accelerators of gradual solar energetic particles (SEPs) in the inner heliosphere. On 2023 March 13, a halo CME, as seen from the Solar and Heliospheric Observatory (SOHO) and the Sun TErrestrial Relations Observatory (STEREO), gave rise to a strong SEP event. In this work, we aim to analyze this CME-driven shock from multiple spacecraft, using both remote-sensing observations from STEREO-A/COR2 and in situ data from the Parker Solar Probe (PSP), Solar Orbiter (SolO), and Wind. In order to determine its direction of propagation and kinematic properties, we model the shock geometry using STEREO-A/COR2 and SOHO Large Angle and Spectrometer Coronagraph (LASCO)/C3 observations as an expanding ellipsoid. The density compression ratio of the shock is determined by fitting the brightness profile from the coronagraphic images with that obtained from raytracing simulations of a double-Gaussian shock-density profile. We compare physical quantities such as compression ratio and Alfvénic Mach number derived from remote-sensing observations with in situ measurements by PSP, SolO, STEREO-A, and Wind. From STEREO-A/COR2, we determine the compression ratio around the entire shock front in the corona, finding significant inhomogeneities that can impact the values found during in situ crossings. Following the evolution of the parameters characterizing the CME from the source to space, we find that closer to the Sun both the gas compression ratio and the Alfvénic Mach number remain almost constant, while they increase at larger radial distances. This indicates a nontrivial evolution of the shock parameters during its journey through the interplanetary space.

The properties of solar wind are closely related to its source region in the solar atmosphere. Here, we investigate the variability of solar wind measured by Parker Solar Probe (PSP) during Encounter 7 (E7) and connect it to spatiotemporal changes in magnetic connectivity to multiple solar sources in the solar atmosphere. During E7, PSP sequentially detected fast solar wind (FSW), Alfvénic slow solar wind (ASSW), and magnetic-velocity alignment structures (MVAS; with high magnitude of the magnetic field and velocity correlation coefficient C_vb and moderately negative normalized residual energy σ_r). ASSW and MVAS both have ∣C_vb∣ ∼ 1 but differ in σ_r. We trace back to the solar atmosphere by applying potential field source surface modeling and ballistic backmapping, and find that FSW, ASSW, and MVAS belong to three distinct regions. Combining these results with EUV observations from SDO/AIA and Hinode/EUV Imaging Spectrometer, we find that magnetic footpoints in the first region oscillate between the center and boundary of a coronal hole, corresponding to variable solar wind containing FSW and MVAS. In the second region, footpoints lie on the western side of NOAA active region (AR) 12796, evidenced by open field lines, enhanced EUV intensity on the AIA map, and blueshifted Doppler velocity, indicating that ASSW may originate from the AR. Footpoints in the third region are primarily located in a quiet Sun region, a possible MVAS source region. These findings highlight the complex and dynamic linkage between solar wind variability and its diverse source regions.

Statistical studies of protoplanetary disks and exoplanet populations often exhibit a “missing mass” problem, where the observed dust masses in (sub)millimeter surveys are significantly lower than expected when compared to the masses of exoplanetary systems. We investigate how the streaming instability and subsequent planetesimal formation in protoplanetary disks might solve this missing mass problem when (sub)millimeter observations are usually interpreted under the assumption of optically thin emission. We conduct hydrodynamical simulations of the streaming instability with self-gravity, after which radiative transfer calculations with dust scattering are performed to measure the (sub)millimeter intensity. The measured intensity is then used to estimate the disk mass under the assumption of optically thin emission and compared to the true mass in the simulation to calculate the observational bias via the mass excess. We find that the emission from overdense filaments that emerges due to the streaming instability is optically thick at (sub)millimeter wavelengths, leading to mass excess factors of ∼2–7.

Radiative shocks are fundamental in astrophysical phenomena, particularly in novae ejecta, where interactions between fast and slow outflows lead to double-shock structures (DSSs). However, direct observations of these shocks remain challenging due to their deep embedding within the ejecta and their small cooling layer. Hydro-radiative simulations with the RAMSES code taking radiative cooling into account are used to model the evolution of DSSs. Additionally, an analytical framework is developed to validate simulation results and predict key shock parameters. Simulations reveal significant cooling effects behind the forward shock, leading to strong density and temperature gradients. The analytical model successfully reproduces these results and enables a detailed parametric study, highlighting the influence of main parameters. Finally, using scaling laws, we miniaturize the DSS to a laboratory scale, preserving key dimensionless parameters that govern the DSS dynamics. By combining simulations, theoretical modeling, and scaling laws, this study paves the way for direct investigation of radiative shocks. It offers a unique opportunity to refine our understanding of astrophysical shock dynamics and validate current models.

We construct mass models of Milky Way dwarf spheroidal galaxies to place constraints on the central black hole masses they can host. We model the galaxies as a three-component system consisting of the stars, dark matter halo, and a central black hole, using the Osipkov–Merritt–Cuddeford class of the anisotropic distribution function. The posterior distribution of black hole mass remains flat toward the low-mass end, indicating that the kinematic data places an upper limit on the black hole mass. Our analysis yields a 95% credible upper limit of . We combine our results with black hole mass measurements and upper limits from the literature to construct a unified M_•–σ_* relation spanning σ_* ∼ 10–300 km s⁻¹, described by , with an intrinsic scatter of σ_int = 0.55. We compare the inferred limits to models of black hole growth via momentum-driven accretion and stellar capture, which predict black hole masses in the range 10³–10⁴M_⊙ for the range σ_* ∼ 6–12 km s⁻¹, in close agreement with the M_•–σ_* relation within the 95% credible upper limits on the black hole masses derived in this work.

CD-35 2722 B is an L dwarf companion to the nearby, ∼50–200 Myr old M1 dwarf CD-35 2722 A. We present a detailed analysis of both objects using high-resolution (R ∼ 35,000) K-band spectroscopy from the Keck Planet Imager and Characterizer combined with archival photometry. With a mass of (planet-to-host mass ratio 0.05) and projected separation of 67 ± 4 au from its host, CD-35 2722 B likely formed via gravitational instability. We explore whether the chemical composition of the system tells a similar story. Accounting for systematic uncertainties, we find dex and for the host, and dex, , and C/O = 0.55 ± 0.01 (stat) ± 0.04 (sys) for the companion. The chemical compositions for the brown dwarf and host star agree within the 1.5σ level, supporting a scenario where CD-35 2722 B formed via gravitational instability. We do not find evidence for clouds on CD-35 2722 B despite it being a photometrically red mid-L dwarf and thus expected to be quite cloudy. We retrieve a temperature structure that is more isothermal than models and investigate its impact on our measurements, finding that constraining the temperature structure to self-consistent models does not significantly impact our retrieved chemical properties. Our observations highlight the need for data from complementary wavelength ranges to verify the presence of aerosols in likely cloudy L dwarfs.

Magnetic reconnection is an important origin of high-energy multispecies ions in the heliosphere, and the interaction of multiple current sheets in reconnection around the kinetic scale is inevitable because of magnetic convection and braiding. Here, we perform hybrid particle-in-cell simulations with kinetic ions and fluid electrons to study the multispecies ion acceleration in this multiple current sheet interaction process. We show that the interaction between multiple current sheets can spontaneously drive turbulence, inducing a power law of −7/3 for the magnetic energy spectrum. We find that both the early reconnection stage and the subsequent turbulence stage can efficiently accelerate ions, with the maximum energy per nucleon species independently increasing as , and we have also reproduced the observed power-law , where Q and M are, respectively, the ion charge and mass. Comparing the two stages, we find that the acceleration efficiency in the turbulence stage is higher, with index γ being approximately twice that of the reconnection stage and index α being smaller, indicating that the turbulence can more efficiently accelerate heavier ions with smaller Q/M, and these characteristics are not sensitive to plasma β. We demonstrate that the underlying physics is that the magnetic structure in the turbulence stage has a statistically larger curvature, thereby enhancing the dominant Fermi acceleration. Our results highlight the crucial role of multiple current sheet interactions and the resulting turbulence in multispecies ion acceleration, and will have multiple potential implications on the origin of energetic ions observed in the heliosphere.

Optical aberrations and instrument resolution can affect the observed morphological properties of features in the solar atmosphere. However, little work has been done to study the effects of spatial resolution on the dynamical processes occurring in the Sun’s atmosphere. In this work, owing to the availability of high-resolution observations of a magnetic pore captured with the Interferometric BIdimensional Spectrometer mounted at the Dunn Solar Telescope, we studied the impact of the diffraction limit and the sampling of an instrument on line-of-sight Doppler velocity oscillations. We reported a noticeable shift in the dominant frequency band from 5 to 3 mHz, as both the angular and detector resolutions of the instruments were degraded. We argue that the observed behavior is a result of the increased contamination of straylight from neighboring quiet Sun regions, masking the true behavior of umbral oscillations. These results suggest that the wave energy contributions reported in the literature and based on low-resolution instrumentation may be fundamentally underestimated. As we move into the era of high-resolution instrumentation such as DKIST and MUSE, this paper will offer a critical baseline for interpreting new observations, especially in terms of distinguishing true dynamic behaviors from artifacts introduced by instrument-related limitations.

This study reports for the first time the occurrence of electrostatic solitary waves during a reconnection exhaust event observed by NASA’s Mars Atmosphere and Volatile Evolution mission on 2015 February 9 in the dayside Martian magnetosheath region. A total of seven burst events were analyzed, showing that the peak amplitudes of most solitary structures lie in the range of 1–4 mV m⁻¹, with pulse durations between 0.3 and 0.7 ms. The generation mechanism of these nonlinear waves is modeled by treating the reconnection exhaust region as an unmagnetized, multicomponent plasma composed of fluid H⁺, O⁺, , and ions along with background superthermal electrons. The Sagdeev pseudopotential technique is used to analyze solitary waves with arbitrary amplitude. The theoretical model predicts positive potential ion acoustic solitons having bipolar electric fields with amplitudes of (1.4–3.4) mV m⁻¹ and having pulse durations of (0.3–0.5) ms, which are in good agreement with the observed values in the reconnection exhaust region.

Using the photon-ion merged-beams technique at the PETRA III synchrotron light source, we have measured cross sections for double and up to tenfold photoionization of La⁺ ions by a single photon in the energy range 820–1400 eV, where resonances and thresholds occur that are associated with the excitation or ionization of one M-shell electron. These cross sections represent experimental benchmark data for the further development of quantum theoretical methods, which will have to provide the bulk of the atomic data required for the modeling of nonequilibrium plasmas such as kilonovae. In the present work, we have upgraded the Jena Atomic Calculator and pushed the state-of-the-art of quantum calculations for heavy many-electron systems to new limits. In particular, we have performed large-scale calculations of the La⁺ photoabsorption cross section and of the deexcitation cascades, which set in after the initial creation of a 3d hole. Our theoretical results largely agree with our experimental findings. However, our theoretical product-ion charge-state distributions are somewhat narrower than the experimental ones, which is most probably due to the simplifications necessary to keep the cascade calculations tractable.

We present the results of simulations of nucleosynthesis in a core-collapse supernova including the neutrino process. Using the Si layer of a 13M_⊙ zero-metal progenitor as the initial composition, we calculate the nucleosynthesis by adopting the temperature, density, neutrino flux, and duration of nucleosynthesis as arbitrary parameters and compare the results with the observed abundance ratios of Sc, Ti, and V in very-metal-poor (VMP) stars taken from the Stellar Abundances for Galactic Archaeology database. As a result, for the first time, we identify the quantitative requirements on local physical conditions. To reproduce the abundance ratios in the VMP stars, the explosive nucleosynthesis should take place under the neutrino exposure, which is the time integration of the neutrino flux, of σ_ν ∼ 10³⁵ erg cm⁻² and temperature of 2.0 GK ≤ T ≤ 3.2 GK. The dependence on the density and each value of the neutrino flux and the duration of nucleosynthesis is weak. We also discuss whether the quantitative requirements are realized during the explosion. Although the requirements are difficult to realize in the one-dimensional simulations, the nonmonotonic thermal evolution shown in recent three-dimensional simulations may satisfy them. Because the evolution is likely caused by turbulent motion stemming from the initial asphericity of the progenitor, it is important to calculate the long-term three-dimensional supernova explosion of multidimensional metal-free progenitor models and follow the nucleosynthesis self-consistently.

The kinematic evolution of hypercompact (HC) H ii regions around young high-mass stars remains poorly understood due to complex interactions with parental environs. We present Querying Underlying Mechanisms of Massive Star Formation with Atacama Large Millimeter/submillimeter Array–Resolved Gas Kinematics and Structures (ALMA-QUARKS) 1.3 mm and ATOMS 3 mm observations (the highest resolution is ∼0.01 pc) of a deeply embedded HC H ii region (diameter ∼ 0.015 pc, electron density ∼ 2 × 10⁵ cm⁻³) exhibiting a striking ≳20 km s⁻¹ global redshift seen in optically thin H30α and H40α recombination lines relative to its parental hot molecular core within a hub–filament system. The 1.3 mm continuum data reveal a distinct 0.1 pc arc and a perpendicular 0.04 pc tail. We propose that this morphology arises from a dynamic champagne flow: the slow expansion of an HC H ii region into a preexisting filament forms an arc and associated low-velocity (few kilometers per second) SiO shocks. Meanwhile, in the opposite direction ionized gas escapes along a steep density gradient traced by a tail and high-velocity (20 km s⁻¹) SiO emission. We reject the bow shock scenario in which ionized gas comoves with a runaway high-mass star because shocked gas in the arc aligns with the hub velocity, contradicting the bow shock prediction. Non-LTE radiative transfer modeling further rules out infall of ionized gas as the velocity shift origin. We conclude that this exceptional HC H ii region is undergoing a few-thousand-year transition phase of “hatching out of the egg:” the ionized gas of the HC H ii region has just broken out of its parental hot core and now is flowing outward supersonically. This work highlights how anisotropic density distributions induce supersonically anisotropic ionized flows that govern HC H ii region evolution.

The formation of the Universe’s first luminous stellar structures depends on the unique conditions at “Cosmic Dawn,” which are set by the underlying cosmological model and early baryonic physics. Observations suggest that high-z star clusters reached stellar surface densities above 10⁵ M_⊙ pc⁻², suggesting scenarios where models predict that the ability of stellar feedback to counter gravitational collapse is severely limited. We investigate the first star clusters in a suite of AREPO simulations, which explore the capacity for ΛCDM halos to maximally form high-density systems without feedback. We include the effects of the supersonic baryon–dark matter streaming velocity, an effect that impacts gas density and distribution in early minihalos. We show that early star clusters can reach high densities even in regions of strong supersonic streaming, provided feedback is weak. We analyze the interplay of the stream velocity and the dynamical processes of structure formation, finding that JWST has the opportunity to detect the brightest, most massive objects in our computational box. The detection of individual z ≥ 12 Population III star clusters below 10⁷ M_⊙ is challenging, although lensing could reveal these objects in rare configurations, especially if a top-heavy initial mass function is present. We find that accounting for baryonic clusters separately from dark matter halos complicates predictions for the faint end of the high-z UV luminosity function, with competing effects from the stream velocity and low-mass clusters outside of halos. Finally, we explore clustering of star clusters as a promising probe of the stream velocity in these systems.

The TIRAMISU code, a new program for computing on-the-fly non-LTE molecular spectra and opacities for solving self-consistent radiative transfer problems in exoplanet atmospheres, is presented. The ultra-hot Jupiter KELT-20 b is used as a case study to identify the wavelength regions at which non-LTE effects may be detectable. It is shown that upper atmospheric OH in vibrational non-LTE should be observable primarily via hot bands in the mid-infrared and enhanced photodissociation in the visible. Varying the abundance of OH in non-LTE demonstrates a nonlinear relationship between the abundance and the strength of non-LTE effects. Using recent calculations of the photodissociation probabilities of OH, it is shown that non-LTE effects can increase the total photodissociation rate by 2 orders of magnitude in the upper atmosphere, which is likely to have a significant impact on atmospheric and chemical modelling. Increases and reductions in the molecular opacities under non-LTE conditions may lead to the mischaracterization of molecular abundances in retrievals that only consider opacities computed under LTE. Collisional data requirements to support future non-LTE modeling for a variety of exoplanet atmospheres and across a wide range of wavelengths are discussed.

The Solar Orbiter spacecraft crossed Comet Leonard’s ion tail on 2021 December 17 near 1 au. In and near the ion tail, significant amounts of singly charged oxygen (O⁺) ions were detected by the Heavy Ion Sensor on board the spacecraft. These ions are likely the result of outgassed water molecules from the comet that became ionized and disassociated into protons and O⁺ ions and that were then picked up by the interplanetary magnetic field and advected outward with the solar wind. At this time, the spacecraft was also located amidst the denser parts of the interstellar helium (He) neutrals that are focused here by their gravitational interaction with the Sun. Pickup He⁺ ions in greater numbers are also found in this region and form when neutrals interact with solar photons. Newly ionized ions can generate waves that propagate mainly along the background magnetic field before the waves scatter the ions toward isotropy. Spectral magnetic field analyses are employed to find mainly elliptically polarized waves associated with O⁺ and He⁺ from ring-beam instabilities. Waves associated with He⁺ are identified, but O⁺ waves are not seen. Visibility is concluded to be affected by the relative amplitude of the waves to turbulence, and the visibility increases when the sampling direction is more aligned with the background magnetic field.

A significant amount of work has been devoted to the study of small binary solar system objects. The majority of these binaries, especially among the near-Earth or main belt asteroids, have small radius ratios, implying a large difference in size between the primary and its companion. Farther from the Sun, the binary fraction increases, with the Kuiper Belt having many known binaries with radius ratios of order unity. In this paper, we consider the runaway growth of a binary system in an accretionary stream of small particles. We perform brute-force integrations, each with 10 million test particles, and numerically compute the gravitational cross sections for each member of the binary as a function of the system’s separation and mass ratio. We show that the behavior of the cross section is complex, and it can be either diminished or enhanced depending on the orbital configuration. In regimes where gravitational focusing dominates the accretion process, we show that binaries grow toward smaller mass ratios than would be expected given single-body cross sections. Finally, we provide a grid of these cross sections for use in future studies of such systems.

Stars embedded in the inner parsec region of an active galactic nucleus (AGN) experience extreme accretion conditions that significantly alter their evolution. We present one-dimensional MESA simulations of stars growing and decaying within AGN disks, implementing radiative-feedback-regulated accretion, limiting stellar growth near the Eddington luminosity, as well as wind-driven mass loss. Unlike stand-alone stars in the field, these embedded stars follow unique evolutionary tracks with well-determined mass evolution and chemical yields. We distinguish two regimes: “immortal” stars that indefinitely remain on the main sequence due to efficient hydrogen mixing; and “metamorphic” stars whose growth is limited by feedback, ultimately enriching the disk with heavy elements upon hydrogen and helium exhaustion in their cores. Results indicate that embedded stars in AGN disks can attain large masses, but radiative feedback, gas retention, and limited mixing likely ensure the “immortal” track is unsustainable. Embedded metamorphic stars significantly enrich AGN disks with helium and α-elements, potentially explaining the observed high metallicity in broad-line regions (BLR) without excessive helium enrichment. This study underscores the critical interplay between stellar feedback and accretion physics in shaping the stellar populations and chemical evolution within AGN disks.

We study the luminosity function (LF) and clustering properties of 888 Hα emitters (HAEs) at 3.75 < z < 6 in the GOODS-N field. The sample, built from JWST CONGRESS and FRESCO NIRCam grism surveys using a novel redshift assignment algorithm, spans ∼62 arcmin² and reaches L_Hα ∼ 10^41.2 erg s⁻¹. We identify two prominent filamentary protoclusters at z ≈ 4.41 and z ≈ 5.19, hosting 98 and 144 HAEs, respectively. The observed Hα LFs show similar shallow faint-end slopes for both protocluster and field galaxies at 3.75 < z < 5, and for the protocluster at 5 < z < 6 (α ≈ −1.2 to −1.3). In contrast, the field LF at 5 < z < 6 has a much steeper slope (), suggesting that protocluster galaxies at z > 5 are more evolved, resembling the populations at 3.75 < z < 5. The observed star formation rate density from Hα integrated down to 0.45 M_⊙ yr⁻¹, is at 3.75 < z < 5 and at 5 < z < 6, with protoclusters contributing about 25% and 55%, respectively. This implies a large fraction of star formation at z > 4 occurs in protoclusters. For the first time, we conduct the star formation-rate-limited three-dimensional clustering analysis at z > 4. We find that the filamentary geometry of protoclusters flattens the power-law shape of the HAE autocorrelation functions, with slopes much shallower than the typically assumed value. The autocorrelation function of field HAEs has a correlation length of at z ≈ 4−5 and at z ≈ 5−6. Comparing the observed correlation functions with the UniverseMachine simulation, we infer the dark matter (sub-)halo masses of HAEs to be at z ≈ 4−6, with a scatter of 0.4 dex.

Compact galaxy groups are ideal laboratories for studying the effects of interactions between active galactic nuclei (AGN) and multiple nearby galaxies. Recent JWST observations of the nearby compact group Stephan’s Quintet highlight tidal flows between the interacting galaxies as well as outflows from the active galaxy NGC 7319. To study the kinematics on a large scale throughout the group, we obtained spatially resolved long-slit spectra of Stephan’s Quintet at multiple slit positions with Apache Point Observatory’s Kitt Peak Ohio State Multi-Object Spectrograph. We fit multiple Gaussians to the Hα λ6563 and [N II] λλ6548, 6583 emission lines to isolate the different kinematic components. We used the kinematics to develop the first biconical outflow model of the narrow-line region of NGC 7319. Using a combination of galactic rotation models, biconical outflow models, and kinematic maps of the ionized gas, we disentangled the outflows, rotation, and tidal flows in the group. We found outflow radial velocities up to 550 km s⁻¹ peaking at 2.6 kpc from the central supermassive black hole, and a transition from AGN-powered outflows to gravitationally powered tidal flows at a projected distance between 2.4 and 6.3 kpc. We performed a line ratio analysis and determined the gas shows Seyfert-like ionization out to 6.3 kpc (projected), which supports our finding that gas outside this radius is predominantly powered by tidal flows. Our separation of kinematic components in Stephan’s Quintet will enable future studies of the physical conditions and dynamical forces in the ionized gas to better quantify the feeding and feedback processes of AGN in compact groups.

Spectral line analysis is essential for investigating the solar atmospheric dynamic processes. Modeling the line profiles provides key insights into plasma motions and variations in temperature and density. This study aims to enhance the parameter estimation of spectral line profiles observed by the Interface Region Imaging Spectrograph through the application of an ensemble approach within the Bayesian Markov Chain Monte Carlo (MCMC) framework. We analyze silicon ion lines (Si IV 1394 and 1403 Å) for samples in the plage, flaring/nonflaring active regions, coronal hole, and boundary of coronal hole and quiet Sun, fitting them with single-Gaussian, double-Gaussian, and Voigt models using the Bayesian MCMC approach. The performance of the model is assessed using statistical metrics, including the reduced chi-square (χ²), Akaike information criterion, and Bayesian information criterion. The Bayesian MCMC method not only provides precise parameter estimates with associated uncertainties but also converges efficiently when initialized with Levenberg–Marquardt least-squares results. Overall, this approach enhances the accuracy of spectral line modeling and model selection, contributing to a more detailed understanding of solar atmospheric dynamics.

We report the discovery of 19 new pulsars identified from archival observations of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) within Galactic latitudes ∣b∣ < 5° and declinations decl. < −5°. The dataset was recorded using FAST’s L-band 19 beam receiver and covered ∼3.6 deg² with a cumulative integration time of ∼500 hr and a total raw data volume of ∼700 TB. Our search employed fast Fourier transform (FFT)–based and fast folding algorithm (FFA)–based periodic searches and the single-pulse search. These new pulsars have spin periods ranging from 0.03 to 5.54 s. Two have periods under 0.1 s, suggesting they are likely young pulsars or mildly recycled pulsars. Four pulsars exhibit dispersion measures (DMs) exceeding 1000 pc cm⁻³, with PSR J1839–0558t having the highest value in our sample at ∼1271 pc cm⁻³, providing valuable samples for pulsar studies in the high-DM regime. Two rotating radio transients, PSRs J1836–0552t and J1847–0624t, were detected by FFA and single-pulse searches but failed with the FFT-based searches. In addition, three faint pulsars that were also missed by FFT-based searches were successfully detected using FFA. These discoveries demonstrate the critical role of FFA in uncovering faint, long-period, and sporadic pulsars and highlight the significant potential of FAST archival data, especially when combined with longer integration times and complementary search techniques, to reveal rare and weak pulsar populations.

The nature of the supernova remnants (SNRs) 3C 397 and W49B has long been a subject of debate, with prior studies offering conflicting interpretations between thermonuclear and core-collapse scenarios. To help settle this debate, we present a systematic, spatially resolved, spectroscopic analysis of both remnants using XMM-Newton. By applying multicomponent thermal models, we derive key physical properties including elemental abundances, ejecta temperatures, ambient densities, and explosion energetics. We compare the inferred metal abundance ratios to a wide range of core-collapse and thermonuclear nucleosynthesis models, including new models whose explosion energies differ from the canonical value of 10⁵¹ erg. We find that the observed Fe/Si and Ca/Si ratios in both SNRs are best matched by certain thermonuclear models. However, no model fully reproduces the complete set of observed abundance patterns. In 3C 397, high Fe enrichment and spatial abundance variations suggest interaction with a dense progenitor environment, and W49B’s composition is overall consistent with a thermonuclear origin; however, both require a low-energy (∼10⁵⁰ erg) supernova explosion. We additionally map the Fe Kα line centroid energies and find a spread, with W49B falling within the core-collapse region—highlighting both environmental complexity and the limitations of this diagnostic for supernova classification. Our results highlight the need for caution in relying on any single diagnostic or nucleosynthesis model for supernova typing, underscore the need for improved nucleosynthesis models, and motivate future high-resolution, high-throughput observations.

Plasmas in various astrophysical systems are in nonequilibrium states, as evidenced by direct in situ measurements in the solar wind, solar corona, and planetary environments, as well as by indirect observations of nonthermal sources of waves and emissions. Specific to observed nonequilibrium plasmas are non-Maxwellian velocity distributions with suprathermal tails, most often described by kappa (power-law) distributions. In this paper, we introduce an alternative modeling for linear waves in plasmas described by the generalized Druyvesteyn distribution model. This model can reproduce not only high-energy tails, but also low-energy flat tops in velocity distributions, like those of electrons in interplanetary shocks and the solar transition region. The wave dispersion relation of longitudinal waves is derived in terms of the newly introduced Druyvesteyn dispersion function. The dispersion curves as well as damping rates of high-frequency Langmuir waves are numerically computed for the isotropic case, and their analytical approximations are provided in the limit of weak damping. We thus offer a new tool for modeling longitudinal waves, and in particular Langmuir waves under the specific conditions of Druyvesteyn distributions.

HESS J1809–193 is an unassociated very-high-energy γ-ray source located in the Galactic plane. The source with a distinctive morphology and spectrum has an extension of 062 with a compact component (r ≤ 01). To explain its multiwavelength emission, we develop a self-consistent, spatially dependent, multizone leptonic model. The system is assumed to be spherically symmetric, with electrons injected near the pulsar termination shock and their subsequent evolution described by a Fokker–Planck-type transport equation. The evolution of the electrons includes convection, diffusion, adiabatic losses, and radiative losses. With suitable parameters, the model reproduces the observed multiwavelength fluxes of HESS J1809–193 reasonably well. The fit indicates that the compact component shows well-developed synchrotron and inverse Compton emission characteristics of a pulsar wind nebula (PWN), whereas the extension exhibits a halo-like morphology without a corresponding synchrotron counterpart, suggesting that the source is transitioning from a PWN to a TeV halo.

The line-of-sight magnetic field of galaxy clusters can be probed using Faraday rotation measure (RM) data. However, our understanding of cluster magnetism is limited due to the scarcity of polarized background radio sources, with most previous studies being constrained to ∼10 sources per cluster. Leveraging the increased source density of the POlarisation Sky Survey of the Universe’s Magnetism, we probe the magnetic field properties of the galaxy cluster A3581 with 111 RMs. We find that the standard deviation in the RM declines monotonically with increasing radius up to 0.75 Mpc, agreeing with a radially declining magnetic field and electron density profile modeled as Gaussian and lognormal random fields, respectively. We compare our observations of the inner 0.75 Mpc of A3581 to various semianalytic models of the magnetic field and electron density and obtain several best-fit models. For the first time, we compare the observed RMs in a cluster to full magnetohydrodynamic simulated clusters from TNG-Cluster and find that the nonmonotonic trend in RM standard deviation past 0.75 Mpc in A3581 is likely caused by past or present merger activity. We identify a possible candidate for a merger to be the galaxy group [DZ2015b] 276, which would be the first group detected in RMs that is not strongly emitting in X-rays. We find a possible merger axis of A3581 with this group at a position angle of θ = 52 ± 4 deg.

Solar flares emit X-rays and high-energy (MeV to GeV) ions called solar energetic particles (SEPs). Astronomical observations show solar-mass protostellar fluxes are a factor Φ ≈ 3 × 10²–3 × 10³ times higher than the present-day Sun. Constraining Φ in the early solar system is important for modeling ionization in the Sun’s protoplanetary disk, the extent of magnetorotational instability or magnetocentrifugal outflows, or even production of short-lived radionuclides. Recent interpretations of meteoritic data—including cosmogenic Ne in hibonite grains, initial ratios in Ca-rich, Al-rich inclusions (CAIs), or even inferences of live ⁷Be in CAIs—suggest values Φ > 10⁵, reaching as high as Φ ≈ 6 × 10⁶, which would make the young Sun extraordinarily active, even for a protostar. We constrain Φ by reexamining these data. We conclude that cosmogenic Ne was produced in hibonite grains as they resided in the disk; ³⁶Cl was created in Cl-poor grains after the disk dissipated; ¹⁰Be was inherited from the molecular cloud, with almost no (<1%) ¹⁰Be created in the disk; and there is no evidence whatsoever for any live ⁷Be in CAIs. We show these data are consistent with a value Φ ≈ 3 × 10³ for the first >5 Myr of the solar nebula. The early Sun evidently emitted a flux of X-rays and SEPs not atypical for a protostar.

We report a series of images of Tycho’s supernova remnant at eight epochs extending over 30 yr: 1986–2016. In addition to our Hα images, we have obtained matched continuum images, which we subtract to reveal faint emission, including a far more extensive network of optical knots and filaments than reported previously. The deepest images also show an extremely faint, fairly diffuse arc of emission surrounding much of the circumference of Tycho to the southeast and south, coinciding with the rim of the radio and X-ray shell. We have measured proper motions for 46 filaments, including many fainter ones near Tycho’s outer rim. Our measurements are generally consistent with previous ones by K. W. Kamper & S. van den Bergh, but ours have far greater precision. Most optical filaments at the shell rim have expansion indices reasonably consistent with the Sedov value (0.40), while the interior filaments have somewhat smaller values, as expected. From the combination of the proper motions of the filaments at the shell rim and the shock velocity at the same positions, one should be able to calculate the distance to Tycho by simple geometry. Determination of the shock velocity from broad Balmer-line profiles is subject to model uncertainties, but the availability of dozens of such filaments with a range of conditions offers the possibility to substantially improve the distance determination for Tycho.

We investigate the origin of the unidentified, extended TeV source 1LHAASO J0500+4454, considering three possible origins: cosmic rays interacting with a molecular cloud (MC), particles accelerated in a currently undetected supernova remnant (SNR), and an energetic outflow powered by a pulsar. Upper limits on the CO and X-ray emission from the γ-ray emitting region disfavor the MC and SNR scenarios, respectively. If a nebula of inverse Compton scattering e^±powers 1LHAASO J0500+4454, then spectral energy distribution modeling indicates that the current particle energy in the nebula is ∼4 × 10⁴⁸ erg. If the coincident magnetar SGR 0501+4516’s rotational energy powered 1LHAASO J0500+4454, then a conservative energy budget calculation requires an initial magnetar spin period P₀ ≲ 5 ms and a spin-down timescale τ_sd ≲ 30 yr, which has implications for the origins of magnetars.

JWST has revealed a population of broad-line active galactic nuclei at z > 4 with remarkably red colors, so-called “Little Red Dots” (LRDs). Ubiquitous Balmer breaks suggest that they harbor old stellar populations in massive, compact host galaxies. We present Atacama Large Millimeter/submillimeter Array observations of three LRDs at z = 3.10, 4.46, and 7.04, targeting molecular and neutral gas via CO(7–6) and [C i](2–1), respectively. We do not detect CO in any target, placing conservative limits on the host molecular gas mass of ≲(1–5) × 10¹⁰M_⊙. We report the tentative (∼3.5σ) detection of the [C i](2–1) line in A2744-45924 (z = 4.46), one of the brightest known LRDs. The [C i] line is narrow (FWHM ∼ 80 km s⁻¹), implying a dynamical mass ≲10¹⁰M_⊙, adopting conservative limits for the size of the galaxy. The dynamical mass limit is significantly lower than expected from the local M_BH–M_dyn relation, and is an order of magnitude below the stellar mass derived from spectral energy distribution fitting, potentially supporting a nonstellar origin of the Balmer break. These results, while tentative, paint a picture of LRDs that is markedly different than typical high-z quasars, which live in massive, gas-rich, and actively star-forming host galaxies.

We present the initial high-resolution X-ray spectroscopic observations of the Fe–K absorption structure in the luminous nearby quasar PG 1211+143, utilizing the X-ray Imaging and Spectroscopy Mission (XRISM). The primary objective is to characterize the Fe–K absorption features due to ultra-fast outflow (UFO) in this Eddington-luminosity source. Observations were conducted with XRISM’s Resolve and Xtend instruments, complemented by simultaneous data from XMM-Newton and NuSTAR. A historically bright phase was captured. The Resolve spectra clearly reveal a prominent P Cygni profile and resolves the Fe–K absorption into six distinct velocity components, ranging from v = −0.074 to −0.405c. A similar superposition of multiple UFOs has been reported in PDS 456, suggesting that such a “UFO forest” structure may be a common feature of near Eddington-luminosity sources. Some UFO components exhibit narrow line widths of approximately σ ∼ 200 km s⁻¹, which may indicate that the outflows have reached their terminal velocities, thereby resulting in a smaller velocity shear. The mass outflow rate is estimated to be , which is of the order of the Eddington accretion rate. This suggests a physically plausible scenario where the outflow is a significant channel for mass ejection.

The dipolarization front (DF) and the flux pileup region (FPR) are crucial downstream structures in magnetic reconnection, where significant energetic electrons are frequently observed. Using a two-dimensional particle-in-cell simulation model, we investigate the formation of energetic electrons in both the DF and the trailing FPR. Our results demonstrate that the energetic electrons at pitch angles near 90° at both regions undergo a two-stage acceleration process: an initial nonadiabatic acceleration by the reconnection electric field at the reconnection site followed by downstream adiabatic acceleration. We find that the 90° pitch-angle energetic electrons in the FPR reach substantially higher energies than those at the DF, since they encounter a stronger reconnection electric field at the reconnection site in the first stage. Furthermore, two populations of energetic electrons with distinct energy ranges at pitch angles near 0° and 180° are identified at the DF. The lower-energy population exhibits energies close to the magnitude of the parallel potential at the DF, which dominates the formation of this population by accelerating the electrons towards the DF and providing the trapping mechanism. The higher-energy population is energized via the Fermi mechanism through multiple reflections within the contracting magnetic island downstream. These findings provide new insights into the generation of energetic electrons during magnetic reconnection.

We present the results of our dynamical state proxy measurements performed on 28 strong lensing galaxy clusters from the Sloan Giant Arcs Survey. Using Chandra ACIS-I/S X-ray data supplemented with HST WFC3 imaging, we measure four morphological parameters: the concentration parameter (c), asymmetry parameter (A), centroid shift (log(w)), and the X-ray-BCG centroid separation (D [kpc]). Our goals are to (A) provide a robust classification of the dynamical state of the clusters in this strong lensing selected sample to enable studies that test various problems in cluster astrophysics and observational cosmology; (B) identify correlations, biases, or disagreements between different measurement proxies and cluster properties; and (C) measure the relaxation fraction (the fraction of clusters classified as relaxed based on X-ray morphology) and compare it to relaxation fractions from cluster samples selected using other methods. We combine the four morphological parameters into a single metric, the combined parameter M, which effectively separates the cluster sample into four dynamical state categories: relaxed, moderately relaxed, moderately disturbed, and disturbed. We find no significant trend in a cluster’s dynamical state with its size, and only a weak, statistically limited dependence on mass and redshift. Based on our classification system, we find that of the clusters are relaxed, which is consistent with relaxation fractions measured for other cluster samples selected on mass-observables. This implies a strong lensing selected sample of clusters is on average dynamically similar to clusters selected via different methods.

Recent optical astrometric and spectroscopic surveys have identified numerous neutron star (NS) candidates in nonaccreting detached binary systems, but their compact-object nature remains unconfirmed. In this work, we present targeted radio observations of 31 such candidates using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), the Robert C. Byrd Green Bank Telescope, and the Shanghai TianMa Radio Telescope. Over a total of 46.65 hr of observing time, we detected neither periodic nor single-pulse radio emissions. These nondetections place stringent upper limits on the flux densities of any potential radio signals, reaching ∼4 μJy for periodic emission and ∼10 mJy for single pulses with FAST. Since our observations are highly sensitive and the flux density upper limits are well below the median fluxes of known Galactic pulsars, this suggests that geometric beaming is the most likely explanation for the nondetections if these objects are indeed pulsars. Alternatively, the NSs may be sufficiently old (≳10 Gyr) and have become intrinsically radio-quiet. In this case, our findings highlight the inherent difficulty of confirming NSs in such old detached binary systems through radio pulsation searches.

We investigate the variability of the east–west asymmetry in energetic storm particle (ESP) heavy ion intensities at interplanetary shocks driven by coronal mass ejections (CMEs) during solar cycles (SCs) 23 and 24. We analyze helium (He), oxygen (O), and iron (Fe) intensities in the energy range of ∼0.13–3 MeV/nucleon, using observations from NASA’s ACE and STEREO missions. We examine the longitudinal distribution of ESP intensities and their correlation with the near-Sun CME speed and average transit CME speed, distinguishing between eastern and western events. Our results reveal significant differences in the east–west asymmetry of ESP intensities between SC 23 and SC 24. This shift is linked to changes in the heliolongitude distribution of the CME Speed Ratio (the ratio of CME average transit speed to near-Sun speed), which transitions from peaking predominantly in the western heliosphere in SC 23 to the eastern heliosphere in SC 24. This shift suggests a systematic difference in CME deflection between the two cycles, with CMEs in SC 23 being, on average, deflected eastward, while those in SC 24 exhibit a tendency for westward deflection.

Recent observations of radio-quiet active galactic nuclei have shown the presence of millimeter emission, whose origin remains unknown, from within parsec scales of the central black hole. We argue that the millimeter emission comes from a spatially extended region that is magnetically connected to the compact X-ray corona, in analogy to the solar wind and corona. We present an analytic model scaled to corona values in which non-equipartition electrons from multiple heights along an extended conical outflow shape the millimeter emission. In this model, the 100 GHz emission originates from within ≲10⁴ gravitational radii (r_g) of the central black hole, though the projected distance from the black hole can be as low as 50r_g depending on the line of sight. Our model predicts a flat emission spectrum and a millimeter-to-X-ray luminosity ratio L_mm/L_X ∼ 10⁻⁴, consistent with observations. These quantities depend weakly on the underlying electron power-law distribution function and black hole mass. We demonstrate this model’s plausibility using a general relativistic magnetohydrodynamic simulation of a thin accretion disc as a case study. Our model highlights the need to study continual dissipation along the outflow to connect the X-ray- and millimeter-emitting regions.

Dust-continuum observations of many protoplanetary disks (PPDs) reveal rings and gaps that are widely interpreted as evidence of ongoing planet formation. Here we present the first framework for inferring planet and disk parameters from such images using variational autoencoder (VAE)-based generative machine learning. The new framework is called Variational Autoencoder for Disks with Embedded Rings (VADER). We train VADER on synthetic images of dust-continuum emission, generated from FARGO3D hydrodynamic simulations postprocessed with Monte Carlo radiative-transfer calculations. VADER infers the masses of up to three embedded planets as well as the disk parameters α-viscosity, dust-to-gas ratio, Stokes number, and flaring index. VADER returns a full posterior distribution for each of these quantities. We demonstrate that VADER reconstructs disk morphologies with high structural similarity (index > 0.99), accurately recovers planet parameters with R² > 0.9 across planet masses, and reliably predicts disk parameters. Applied to Atacama Large Millimeter/submillimeter Array (ALMA) dust-continuum images of 23 PPDs, our model returns mass estimates for embedded planets of 0.3–2 M_Jup that agree to within 1σ of published values in most cases, and infers disk parameters consistent with current literature. Once trained, the VAE performs full posterior parameter inference in a matter of minutes, offering statistical rigor with enough computational speed for application to large-scale ALMA surveys. These results establish VAE-based models as powerful tools for inferring from disk structure the masses of embedded planets and the global disk parameters, with their associated uncertainties.

Coronagraph observations provide key information about the orientation of the Sun’s magnetic field. Previous studies used various algorithms to segment quasi-radial features in coronagraph images and approximate their local plane-of-sky (POS) geometry and orientation, which can be used as input for optimizing and constraining coronal magnetic field models. We present a new framework that allows for further quantitative evaluations of image-based coronal segmentation methods against magnetic field models, and vice versa. We compare quasi-radial features identified from QRaFT, a global coronal feature tracing algorithm, in white-light coronagraph images to outputs of the Magnetohydrodynamic Algorithm outside a Sphere (MAS) model, an advanced MHD model. We use the FORWARD toolset to produce synthetic polarized brightness images coaligned to real coronagraph observations, segment features in these images, and quantify the difference between the inferred and model magnetic field. This approach allows us to geometrically compare features segmented in artificial images to those segmented in white-light coronagraph observations against the POS projected MAS coronal magnetic field. We quantify QRaFT’s performance in the artificial images and observational data, and perform statistical analyses that measure the accuracy and uncertainty of the model output to the observational data. The results demonstrate that a coronal segmentation method identifies the global large-scale orientation of the coronal magnetic field within ∼±10^∘ of the POS projected MAS magnetic field.

In this work, we carry out a systematic search for γ-ray emission from 65 galaxy clusters based on 16 yr of Fermi Large Area Telescope data in the energy range from 500 MeV to 500 GeV. Only two clusters, A2065 and A2244, exhibit significant emission, with local significances of ∼5σ. The test statistic (TS) values are ∼25.4 for A2065 and ∼25.1 for A2244. We investigate a potential dark matter (DM) origin for these signals. The peak TS value of A2065 is ∼26.2 for the DM annihilation channel at a DM mass of m_χ ∼ 25.0 GeV. For A2244, the largest TS value is ∼14.5 for at m_χ ∼ 6.0 GeV. However, the corresponding cross sections conflict with the upper limits derived from observations of dwarf spheroidal galaxies. This indicates that these signals cannot be attributed to DM annihilation. Finally, we consider the γ-ray flux arising from hadronic cosmic-ray (CR) interactions in the intracluster medium, with the corresponding estimated volume-averaged CR-to-thermal pressure ratios being ∼4% and ∼16%, respectively.

Total solar eclipses (TSEs) provide a unique opportunity to observe the large-scale solar corona. The solar wind plays an important role in forming the large-scale coronal structure, and magnetohydrodynamic (MHD) simulations are used to reproduce it for further studying coronal mass ejections (CMEs). We conduct a data-constrained MHD simulation of the global solar corona including solar wind effects of the 2024 April 8 TSE with observed magnetograms using the message-passing interface adaptive mesh refinement versatile advection code (MPI-AMRVAC) within 2.5 R_⊙. This TSE happened within the solar maximum, hence the global corona was highly structured. Our MHD simulation includes the energy equation with a reduced polytropic index γ = 1.05. We compare the global magnetic field for multiple magnetograms and use synchronic frames from the Solar Dynamics Observatory/Helioseismic and Magnetic Imager to initialize the magnetic field configuration from a magnetofrictionally equilibrium solution, called the outflow field. We detail the initial and boundary conditions employed to time-advance the full set of ideal MHD equations such that the global corona is relaxed to a steady state. The magnetic field, the velocity field, and distributions of the density and thermal pressure are successfully reproduced. We demonstrate direct comparisons with TSE images in white light and Fe XIV emission augmented with quasi-separatrix layers, the integrated current density, and the synthetic white-light radiation, and find a good agreement between simulations and observations. This provides a fundamental background for future simulations to study the triggering and acceleration mechanisms of CMEs under solar wind effects.

We introduce an improved and fast inversion tool that is able to provide the thermodynamics of the solar atmosphere from the photosphere to the top of the chromosphere, as well as the integrated radiative losses (IRLs) in the chromosphere for data observed by the Interface Region Imaging Spectrograph (IRIS). This NASA mission has been observing the Sun and providing, among other kinds of data, multiline spectral observations sensitive to changes in the lower solar atmosphere since 2013. In this paper, we explain the new inversion tool IRIS²⁺ based on the IRIS²⁺ database, which is based on 135,472 synthetic representative profiles (RPs), each of them consisting of six chromospheric lines and six photospheric lines, their corresponding representative model atmospheres (RMA), and the IRL associated with these atmospheres. A nearest neighbor (k-nn) model algorithm is trained with the synthetic representative profiles to predict the closest RP in the database to the one observed, at which point IRIS²⁺ assigns the RMA and the IRL to the location of that observed profile. We have compared the results obtained by IRIS²⁺ with results obtained from the state-of-the-art inversion code STiC, which is also used to build the IRIS²⁺ database. We find that the thermodynamics and the IRL obtained with both methods are comparable in most cases. Therefore, IRIS²⁺ is a fast and reliable inversion tool that provides approximate values of the thermodynamic state and the radiative losses in the lower solar atmosphere for a large variety of solar scenes observed with IRIS.

We measure line-of-sight velocities of metal absorption and H I emission along 132 QSO sight lines in order to study gas accretion and outflow at the disk–halo interface of the Milky Way. While previous studies have focused on high- and intermediate-velocity clouds and complexes, we examine material at predominantly low velocities relative to the local standard of rest (i.e., all absorbers at ∣v_LSR∣ < 90 km s⁻¹, and absorbers at 90 < ∣v_LSR∣ < 150 km s⁻¹ not associated with any well-defined cloud complexes). We find that gas accretion velocities in the northern Galactic hemisphere are correlated with the ionization potential energy of the multiphase metal ions we include in our analysis; more highly ionized material traced by C iv , Si iv , and N v is moving toward the disk 10−15 km s⁻¹ faster than low ionization state material traced by S ii , C ii* , and Ni ii . We interpret this dependence as potential evidence of warm accreting gas cooling as it reaches the disk–halo interface, causing a pileup of slower-moving cool gas. We find that with the number of available sight lines, kinematic modeling cannot rule out exponential density distributions or layers of gas that sandwich the Galactic disk. Our results paint a picture of a complex, dynamic disk–halo interface in which low-velocity material likely plays an important role in fueling star formation in the Milky Way.

The LIGO–Virgo–KAGRA collaboration has detected over 150 confirmed gravitational-wave events through Observing Run 4a. Binary black hole (BBH) systems represent the overwhelming majority of these observations. We construct a model for the population of BBHs based on the distribution of metallicities in galaxies and state-of-the-art stellar evolution models implemented through the Stellar Evolution N-body code. We calculate the redshift evolution of the total merger rate of BBHs and the differential rates with respect to primary mass, secondary mass, and the mass ratio. We explore variations in the delay-time distribution’s power-law index and show that it affects the total merger rate’s spectral shape, but primarily acts as an amplitude shift on the differential rates. When comparing to the primary mass distribution, our results indicate that either the average initial mass function in dwarf galaxies must be top heavy, or most of the 30–40 M_⊙ BHs must be formed through a dynamical capture mechanism. For masses greater than about 50 M_⊙, the predicted number of BBH systems plummets to zero, revealing the well-known mass gap due to the pair instability mechanism and mass loss in binary systems.

The ubiquitous 5 minute solar p-mode oscillations, excited at the photosphere, play a crucial role in driving various coronal instabilities and mediating upward energy transport. These modes are strongly influenced by nonthermal electron populations. To investigate this, we employ a double-spectral electronic thermostatistical framework—the generalized (r, q)-distribution—to analyze the oscillation dynamics, growth behavior, and mechanical energy transport properties of longitudinal helioseismic modes at the photosphere. A local linear perturbative analysis, applied to inhomogeneous, viscous, turbulent, and nonthermal solar plasmas, yields a cubic eigenmode equation (dispersion relation) capturing diverse signatures of collective global modes. We examine the influence of nonthermality indices, electron temperature, and ion dynamic viscosity on dispersion and mode stability. Numerical analysis of the coupled dynamics of low-energy (thermal) and high-energy (suprathermal) electrons reveals their significant impact on solar surface oscillations. Notably, the nonthermality spectral indices r and q play mode-accelerating roles, counteracting damping from temperature and viscosity. Our results suggest that the high-frequency (short-period) p-modes can carry energy fluxes exceeding 10⁶ W m⁻² near the lower photosphere—energizing the chromosphere and quiet corona—thereby potentially influencing the excitation of spicules, microspicules, and coronal loop oscillations. In contrast, the low-frequency (long-period) g-modes have no such active influences on coronal heating. A hybrid power-law decay formalism is developed to model the attenuation of p-mode energy flux with height and is quantitatively fitted to Solar Dynamics Observatory/Helioseismic and Magnetic Imager Doppler velocity observations. Complementary 2D simulations further elucidate the spatiotemporal evolution of vertical energy flux, shaped by the nonthermal electron distribution.

Future near-infrared spectroscopic galaxy surveys will target high-redshift emission-line galaxies (ELGs) to test cosmological models. Deriving optimal constraints from ELG clustering hinges on a robust understanding of their environmental dependence. Using the TNG300-1 simulation, we explore the correlation between properties of Hα emitters and their environment anisotropy rather than traditional density-based measures. Our galactic Hα emission model includes contributions from the warm interstellar medium. The environment anisotropy and type are assigned using a halo-mass-dependent smoothing scale. We find that most luminous Hα emitters (L_Hα > 10⁴² erg s⁻¹) reside in filaments and knots. More generally, Hα emitters are more biased in strongly anisotropic environments. While correlations with galactic properties are found to be weak, they are statistically significant for host halo masses M ≲ 10¹²M_⊙h⁻¹. Our analysis motivates further investigation into how environmental anisotropy influences galaxy evolution, and highlights the potential for leveraging these effects in the analyses of upcoming cosmological surveys.

Planets with masses between Earth and Neptune often have radii that imply the presence of volatiles, suggesting that water may be abundant in their interiors. However, directly observing the precise water mass fraction and water distribution remains unfeasible. In our study, we employ an internal structure code, MAGRATHEA, to model planets with high water content and explore potential interior distributions. Departing from traditional assumptions of a layered structure, we determine water and rock distribution based on water–rock miscibility criteria. We model wet planets with an iron core and a homogeneous mixture of rock and water above it. At the outer regions of the planet, the pressure and temperature are below the rock–water miscibility point (the second critical point), causing the segregation of water and rock. Consequently, a shell of water is formed in the outermost layers. By considering the water-rock miscibility and the vapor state of water, our approach highlights the uncertainty in estimating the water mass fraction of detected exoplanets.

The surface densities of star formation, Σ_SFR, in 24 dwarf irregular (dIrr) galaxies from the LITTLE THINGS survey are combined with gas surface densities and midplane pressures to examine the correlations found previously for spiral galaxies. The pressure is the weight of the disk inside the gas layer, including gas, stars, and dark matter, which usually dominates disk gravity in dIrrs. We compare the results to the outer part of M33, which has similar local properties but a slightly higher metallicity, enabling the detection of CO. All the data are convolved to the H I beam, but to study the effects of resolution, the galaxies are examined first with average radial profiles, and then with maps having 15 pixels and 244 pc pixels. The correlations are found to be independent of resolution from 24 to 424 pc. The average ratio of molecular to atomic surface density is estimated to be 0.23 ± 0.1, from the H₂ surface density in M33 compared to the H I surface density at the same Σ_SFR in the dIrrs. With this ratio, the average star formation rate per molecule is about the same for all the dIrrs, and a factor of 2 less than the rate in M33. The pressure in dIrrs is so low that CO is essentially a dense gas tracer, with the same surface density threshold at the low metallicities of dIrrs as HCN has in spiral galaxies. As a result, CO regions in dIrrs should be strongly self-gravitating.

We report the results of an extensive survey in the quest for pulsation signatures in main-sequence M dwarf stars, based on observations acquired by the TESS space mission. Using TESS 2 minutes cadence light curves from a sample of 56,217 targets, observed in Sectors 1–89 of the mission, we identify low-amplitude modulation for 15 targets, with period values ranging from 0.0421 days (∼1.01 hr) to 0.1148 days (∼2.75 hr). These periodicities fall within the predicted range for pulsations in low-mass main-sequence M-type stars. For instance, for low-mass stars, pulsation is a fundamental observable for solving persistent discrepancies between observed and predicted parameters (e.g., radii, masses). Nevertheless, the detection of a pulsating M dwarf has not yet been achieved despite solid theoretical predictions. Among the 15 targets referred to, only one star, the dwarf MGC 2543, appears to be a good candidate for a pulsator, despite a mean modulation amplitude of 1647 μmag, which is higher than the predicted values.

The standard external-shock model, assuming a homogeneous turbulent downstream, has been widely used to decipher the afterglows of gamma-ray bursts. However, such assumption is invalid when the shock encounters a density jump. In this paper, we propose a self-consistent scenario to model the external forward shock emission, involving the advection and decaying behaviors of the shock-generated magnetic fields (sgMFs) in the downstream as found in particle-in-cell simulations. In an interstellar medium, our model is almost returned to the standard model but with . Here, _B describes the sgMFs’ fraction of shock energy in the standard model, t_dyn is the shock dynamic time, and t_B together with α_t depicts the sgMFs’ decaying behavior in our model. The situation is the same for the wind medium but with weak deviation in the early phase. When the shock encounters the density rise/dip, a shallower/deeper decay appears in the light curve. These behaviors are obvious for high-frequency emission or at the phase after the jet break. The GeV emission in the afterglow can serve to probe the circumburst density jump. We apply our model to decipher the later afterglows of the giant flare from SGR 1806-20. It is shown that a fireball propagating into a magnetar bow shock environment can well reproduce the observed peculiar steep decay in the radio light curve at ∼10 days from the burst.

Data-driven stellar classification has a long and important history in astronomy, dating as far back as Annie Jump Cannon’s “by-eye” classifications of stars into spectral types, still used today. In recent years, data-driven spectroscopy has proven to be an effective means of deriving stellar properties for large samples of stars, sidestepping issues with computational efficiency, incomplete line lists, and radiative transfer calculations associated with physical stellar models. A logical application of these algorithms is the detection of unresolved stellar binaries, which requires accurate spectroscopic models to resolve flux contributions from a fainter secondary star in the spectrum. Here, we use The Cannon to train a data-driven model on spectra from the Keck High Resolution Echelle Spectrometer. We show that our model is competitive with existing data-driven models in its ability to predict stellar properties T_eff, R_⋆, [Fe/H], and , as well as the instrumental point-spread function, particularly when we apply a novel wavelet-based processing step to spectra before training. We find that even with accurate estimates of star properties, our model’s ability to detect unresolved binaries is limited by its ∼3% accuracy in per-pixel flux predictions, illuminating possible limitations of data-driven model applications.

Observations by the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) are combined with counterpart Spitzer spectral map data to study the aromatic, aliphatic, and polycyclic aromatic hydrocarbon (PAH) size evolution across the northwest photodissociation region (PDR) of the Iris Nebula (NGC 7023). The 3.3–3.4 μm complex (I_3.3) and 11.2 μm (I_11.2) PAH band strength are determined through direct integration. In addition, the former is decomposed into a 3.3 () and 3.4 μm () subfeature by fitting SPHEREx bandpass-integrated photometry using a modeled, highly sampled, multicomponent spectrum. I_3.3, I_11.2, , and all peak at the PDR. The NASA Ames PAH IR Spectroscopic Database is used to obtain the average number of carbon atoms () and small PAH fraction (f_small) by fitting the isolated PAH component of the Spitzer segment: and 0.24 ≲ f_small ≲ 0.36, respectively. /, I_11.2/I_3.3, , and f_small all show a demarcation that matches the large-scale morphology of the region. For and this is reflected by two distinct trends when plotted against each other, one associated with the dense medium and the other with the diffuse medium: = 0.42 ± 0.01 and = 0.10 ± 0.01, respectively. and f_small are tentatively correlated with I_11.2/I_3.3 (R = 0.54 ± 0.05 and −0.45 ± 0.05, respectively). A wider variety of large(r) extended interstellar medium objects is required to tighten the correlations, turn them into quantitative calibrators for PAH size, and pin down the discrepancy of correlations with involved.

This study is based on proton flux data from ESA’s Solar Energetic Particle Environment Modeling database, analyzing solar energetic particle (SEP) events observed near Earth from 1976 to 2017. We have matched these events with corresponding solar flares and coronal mass ejections (CMEs) to create a comprehensive list of SEP events spanning almost four solar cycles. Using this list, we conduct a statistical analysis of the flare–SEP correlation and SEP timing information. Our findings confirm that SEP events recorded at 1 au are more commonly associated with flares occurring in the western hemisphere of the Sun’s surface. Moreover, we develop an empirical model relating the SEP proton peak flux to the characteristics of flares and CMEs, which works particularly effectively for SEP events triggered by eastern flares. We also verify that flares with higher intensity are more likely to produce SEP events up to higher energies, such as those detected above 100 MeV. In this energy range, more than half of the SEP events are triggered by X-class flares. Finally, we introduce an empirical model that uses the flare longitude to predict the timing of the SEP peak flux, especially for intense flare events. These models can aid in mitigating particle radiation risks for space missions.

SBS 0335-052E is a young star-forming dwarf galaxy with a total stellar mass of M_* ≲ 10⁸M_⊙ and an extremely low metallicity (Z ∼ 1/40Z_⊙), which has long been considered to be devoid of an active galactic nucleus (AGN). Here, we report the detection of temporal flux variability of SBS 0335-052E in near-infrared (NIR) 3–4 μm bands on timescales of several years, showing dimming and brightening of up to 50% over 14 yr, based on archival data from the Wide-field Infrared Survey Explorer. Our spectral energy distribution (SED) fitting of archival ultraviolet (UV)-NIR photometry, including AGN SED models, indicates that the variable NIR emission arises from an edge-on AGN dust torus. The UV-optical emission from the accretion disk is obscured and does not reach us, leading to the dominance of the host galaxy’s young stellar population in the UV-optical wavelengths. This analysis favors the presence of a Compton-thick, heavily obscured AGN in SBS 0335-052E, consistent with its observed X-ray weakness. From the SED fitting, we estimate an AGN bolometric luminosity of L_bol = 1.2 × 10⁴³ erg s⁻¹, which implies a black hole (BH) mass of M_BH ≃ 10⁵M_⊙ if the AGN is accreting at the Eddington limit. If confirmed, SBS 0335-052E would be the least massive galaxy known to host an AGN, likely harboring an intermediate-mass BH.

Coronal mass ejections (CMEs), since their first observation in 1971, have been widely acknowledged as the most significant eruptive phenomena and the primary cause of catastrophic space weather events within our solar system. Whether similar processes involving stellar mass ejections (SMEs) occur on other stars holds immense potential for advancing our understanding of stellar behavior and providing insights into the search for extraterrestrial life. However, detecting SMEs remains challenging, particularly in establishing reliable approaches and diagnostics. Here, we conduct a proof-of-concept Sun-as-a-star experiment using solar CMEs as proxies, analyzing EUV spectral lines from the Extreme Ultraviolet Variability Experiment on board the Solar Dynamics Observatory. By comparing 26 front-side fast CMEs with 14 confined flares of class M 1.0 and above, we find that the Doppler responses in 18.04, 19.51, and 28.42 nm during CME events provide a promising diagnostic to distinguish Sun-as-a-star CME signals from flare features. We further show that CME characteristics can be reasonably reproduced from the Doppler velocities in these three lines, providing a hopeful diagnostic for inferring otherwise unobservable properties of eruptions on remote stars. These findings advance the exploration and understanding of mass ejections in stars. We therefore advocate the resumption of the EUV observations of extrasolar stars.

The 2024 April 8 total solar eclipse provides a unique opportunity to study the solar corona. This work presents our simulations of the solar corona at the time of the eclipse based on magnetohydrodynamic modeling performed with the Alfvén Wave Solar atmosphere Model in the Space Weather Modeling Framework, developed at the University of Michigan. We performed multiple simulations based on photospheric magnetic maps from four sources, i.e., ADAPT-GONG, Lockheed Martin ESFAM-HMI, HipFT-HMI, and NSO-NRT-HMI maps. Our study focuses on how differences in the magnetic field maps affect the coronal magnetic field structure and coronal heating properties in the simulation. The synthesized observables show remarkable differences due to the distinct magnetic coronal topologies, which stem from the different local magnetic flux distributions. We analyze the properties of the open magnetic flux regions of the models. We also study the coronal heating rate in the models. The total volume integrated heating rate yields a difference of 20% across the models. The results also show that the differential emission measure in the high-temperature regions is sensitive to the magnetic field maps. Our findings underscore the importance of comprehensive photospheric magnetic field data in improving future solar coronal models.

Ultracool dwarfs consist of lowest-mass stars and brown dwarfs. Their interior is fully convective, in contrast to that of the partly convective Sun-like stars. The magnetic field generation process beneath the surface of ultracool dwarfs is still poorly understood and controversial. To increase samples of active ultracool dwarfs significantly, we have identified 962 ultracool dwarfs in the latest Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) data release, DR11. We also simulate the Chinese Space Station Survey Telescope (CSST) low-resolution slitless spectra by degrading the LAMOST spectra. A semisupervised machine learning approach with an autoencoder model is built to identify ultracool dwarfs with the simulated CSST spectra, which demonstrates the capability of the CSST all-sky slitless spectroscopic survey in the detection of ultracool dwarfs. The magnetic activity of the ultracool dwarfs is investigated by using the Hα line emission as a proxy. The rotational periods of 82 ultracool dwarfs are derived based on the Kepler/K2 light curves. We also derive the activity–rotation relation of the ultracool dwarfs, which is saturated around a Rossby number of 0.12.

Active galactic nucleus (AGN)-driven outflows are routinely invoked as a key agent of supermassive black holes to regulate the evolution of galaxies. The radial distance from the central engine is a crucial parameter for evaluating the impact of these outflows on the host galaxy. In this work, we estimate the radial distances of UV outflow components in NGC 5548 using the most up-to-date absorption line variability method, combined with multi-epoch Hubble Space Telescope (HST)/Cosmic Origins Spectrograph spectroscopy from the 2014 AGN STORM campaign and archival data observed in 2013. The recombination timescale (t_r) of the absorbers is measured by analyzing the detection rate curves of absorption line variability. In particular, the detection rate curves of the absorption troughs showing blended multiple velocity components are featured by distinct “multistep” profiles, allowing for measuring t_r for individual components. Among the six identified outflow components, four are found to be a few parsecs from the center, and two are 30–40 pc away. Our results agree well with the more reliable results in the literature on components 1 and 4, and show overall consistency with previous works, demonstrating the power of our new methodology, especially when it is aided by densely sampled HST spectra.

Robotic telescope networks play an important role in capturing early and bright optical afterglows, providing critical insights into the energetics and emission mechanisms of GRBs. In this study, we analyze GRB 230204B, an exceptionally energetic and multipulsed long GRB, detected by the Fermi Gamma-ray Burst Monitor and MAXI detectors, with an isotropic equivalent gamma-ray energy exceeding 10⁵⁴ erg. Time-resolved spectral analysis reveals a transition in the prompt emission from hard (sub-photospheric-dominated) spectra during early pulses to softer (synchrotron-radiation-dominated) spectra in later pulses, indicative of a hybrid jet composition. We report the discovery and characterization of the optical afterglow using the Mobile Astronomical System of Telescope-Robots (MASTER) and Burst Observer and Optical Transient Exploring System (BOOTES) robotic telescope networks, which enabled rapid follow-up observations starting at ∼1.3 ks post-burst. The optical luminosity at this time was exceptionally high, surpassing that of many other optically bright GRBs, such as GRB 990123 and GRB 080319B. This places the burst among the most luminous optical GRBs observed to date. Long-term radio observations extending to 335 days post-burst were conducted with the Australia Telescope Compact Array. Multiwavelength modeling, incorporating data from MASTER, BOOTES, Devasthal Optical Telescope, Swift/XRT, and radio observations, was conducted using an external interstellar medium (ISM) forward-shock top-hat jet model with afterglowpy. The results reveal a narrow and highly collimated jet with a circumburst density of n₀ ∼ 28.12 cm⁻³, kinetic energy E_K ∼ 4.18 × 10⁵⁵ erg, and a relatively low value of _B = 2.14 × 10⁻⁶, indicating shock-compression of the magnetic field in the surrounding ISM. We constrained a low radiative efficiency of ∼4.3%. This study highlights the indispensable contribution of robotic networks to early afterglow observations and advances our understanding of GRB 230204B unique characteristics and underlying jet physics.

In this work, we explore the nature of z > 1 galactic bars. Once thought to be highly transient, our results demonstrate otherwise. Our sample consists of nine massive (>10^10.5M_⊙) star-forming barred-spiral galaxies at z_spec ∼ 1.5. Using rest-frame near-IR (F444W) JWST/NIRCam imaging, we apply ellipse fitting along with 1D and 2D morphological modeling to directly measure bar properties. We find that five galaxies host flat surface brightness profiles (bar Sérsic index < 0.4), indicative of highly evolved, “mature” bars. By contrast, only two galaxies show exponential profiles, characteristic of young bars, and these are also shorter in absolute length than the flat bars. We therefore conclude that a large fraction of bars at this epoch have already matured, thereby indicating the presence of well-settled disks required to facilitate bar formation and sustained evolution well before z ∼ 1.5. To assess the gravitational impact of the bars, we calculate the maximum transverse-to-radial force ratio (Q_b). We find that the Q_b values are comparable to, or weaker than, those of bars in the local Universe; seven of the nine bars show only a marginal increase in strength with maturity (from exponential to flat bars). Contrarily however, the remaining two bars are flat, but have the lowest Q_b values in our sample. We hence propose that the mature bars at z ∼ 1.5 may experience phases of weakening due to rapid gas inflows and/or minor mergers. In conclusion, our work sheds light on the rapidly evolving nature of high-z bars and paves the way for larger statistical studies.

Geological evidence indicates that the Moon formed at least 4.46 billion years ago. Models of Earth–Moon evolution generally describe tidal friction as the primary driver of lunar recession—the gradual increase in the lunar orbital semimajor axis—and the corresponding lengthening of Earth’s day. However, tidal dissipation within Earth’s oceans is sensitive to climatic and tectonic boundary conditions, which introduce variability not fully captured in existing models. Here, we develop a probabilistic framework that quantifies lunar recession and its variations by incorporating the influence of climate dynamics, plate tectonics, and geological constraints on Earth’s length-of-day evolution. Applied to the past 1 billion years, the analysis yields an additional, previously unrecognized long-term lunar recession of ∼0.84 mm yr⁻¹, equivalent to an orbital expansion of ∼808 km. This signal is primarily associated with sea-level change acting on the surface of the Earth with evolving plate configurations, with a particularly strong expression during the Cenozoic Era. The revised recession history adds an uncertainty of ∼15 million years to the lunar age. These findings suggest that slightly lower tidal dissipation rates than those used in earlier models provide better agreement with geological constraints on lunar chronology.

The recent launches of the Einstein Probe and the Space Variable Objects Monitor mission have led to the detection of a growing number of long gamma-ray bursts (GRBs) with significant, early soft X-ray flux during their gamma-ray emission, prompting the question of whether their multiband prompt emission shares a common origin in region and mechanism. To address this, we utilize the 20-year Swift archival data, which provides a substantial sample of joint soft X-ray and gamma-ray observations, enabling a systematic joint spectral study. We resolve 110 temporal pulses from 46 GRBs and find that a single power-law model with a low-energy break or cutoff adequately describes the prompt spectra from 150 keV down to 0.5 keV. More than half of the sample pulses require a break around a few keV, with average spectral indices 〈α₁〉 = −0.88 and 〈α₂〉 = −1.46 consistent with synchrotron radiation in a marginally fast-cooling regime. The observed spectral evolution and the distribution of indices support a single-emission-region origin, where the varying spectral shapes are largely governed by the evolution of the synchrotron cooling frequency ν_c and the effect of finite emission width. The observed differences in the temporal behavior between X-ray and gamma-ray light curves can be naturally explained by this spectral evolution across the broad band.

We present a spectroscopic search for broad Hα emitters at z ≈ 3.7–6.5 in the GOODS-N field, utilizing JWST/NIRCam slitless spectroscopy from FRESCO and CONGRESS, complemented by JADES imaging. We identify 19 broad Hα emitters with FWHM > 1000 km s⁻¹ at z ≈ 4–5.5, including nine new sources. The broad Hα luminosity function derived from our sample is consistent with those of other JWST-selected broad-line active galactic nuclei (AGN) reported in the literature. The black hole masses and AGN bolometric luminosities inferred from the broad Hα components indicate that most sources are accreting at ∼10% of the Eddington limit. We derive their host stellar masses via spectral energy distribution (SED) fitting and find higher M_BH/M_* ratios relative to the local M_BH–M_* relations, consistent with previous studies. We find that 42% of the sample do not satisfy the widely used color selection criteria for little red dots (LRDs), with the majority of these sources lacking the characteristic steep rest-optical red slope, indicating that the LRD selection is highly incomplete when selecting AGN galaxies. A comparison of the average SEDs between our sample and LRDs selected in the same field reveals that the steep red slopes observed in some LRDs are likely due to line-boosting effects as previously suggested. Furthermore, we find that 68% of color-selected LRDs with Hα detections in the NIRCam/grism spectra do not exhibit broad-line features. While the limited sensitivity of the grism spectra may hinder the detection of broad-line components in faint sources, our findings still highlight the enigmatic nature of the LRD population.

Fisher-matrix forecasts are presented for the cosmological surveys of the Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS) and the Subaru Prime Focus Spectrograph (PFS). The wide, low-redshift coverage of J-PAS and the high-density, high-redshift mapping of PFS are strongly complementary: combining the two reduces marginalized uncertainties on all primary parameters compared with either survey individually. Adding the joint J-PAS+PFS data to next-generation cosmic microwave background (CMB) measurements from the Simons Observatory and LiteBIRD yields an expected precision of σ(∑m_ν) = 0.017 eV in the ΛCDM+∑m_ν + N_eff framework, sufficient to disfavor the inverted neutrino hierarchy at 2.34σ if the true mass sum equals the normal-ordering minimum. Motivated by recent DESI results, we also forecast within a w₀w_aCDM+∑m_ν + N_eff cosmology, adopting the DESI DR2 best-fit values (w₀ = −0.758, w_a = −0.82) as fiducial. The combination CMB+J-PAS+PFS then delivers σ(w₀) = 0.044 and σ(w_a) = 0.18, corresponding to a 5.1σ preference for a time-varying dark-energy equation of state. These findings show that J-PAS and PFS, especially when coupled with Stage IV CMB observations, will provide competitive tests of neutrino physics and the dynamics of cosmic acceleration.

We present the number density of massive () quiescent galaxies at 2 < z < 5 using JWST NIRSpec PRISM spectra. This work relies on spectra from RUBIES, which provides excellent data quality and an unparalleled, well-defined targeting strategy to robustly infer physical properties and number densities. We identify quiescent galaxy candidates within RUBIES through principal component analysis and construct a final sample using star formation histories derived from spectrophotometric fitting of the NIRSpec PRISM spectra and NIRCam photometry. By inverting the RUBIES selection function, we correct for survey incompleteness and calculate the number density of massive quiescent galaxies at these redshifts, providing the most complete spectroscopic estimates prior to cosmic noon to date. We find that early massive quiescent galaxies are surprisingly common (≳10⁻⁵ Mpc⁻³ by 4 < z < 5), which is consistent with previous studies based on JWST photometry alone and/or in smaller survey areas. We compare our number densities with predictions from six state-of-the-art cosmological galaxy formation simulations. At z > 3, most simulations fail to produce enough massive quiescent galaxies, suggesting the treatment of feedback and/or the channels for early efficient formation are incomplete in most galaxy evolution models.

The relationship between the composition of rocky exoplanets and their host stars is fundamental to understanding planetary formation and evolution. However, previous studies have been limited by inconsistent datasets, observational biases, and methodological differences. This study investigates the compositional relationship between rocky exoplanets and their host stars, utilizing a self-consistent and homogeneous dataset of 21 exoplanets and their 20 host stars. By applying sophisticated interior structure modeling and comprehensive chemical analysis, we identify a potential 1:1 best-fit line between the iron-mass fraction of planets and their host stars equivalent with a slope of and intercept of . This results are consistent at the 1σ level with other homogeneous studies, but not with heterogeneous samples that suggest much steeper best-fit lines. Although our results remain tentative due to sample size and data uncertainties, the updated dataset significantly reduces the number of super-Mercuries from four to one, but it remains that several high-density planets are beyond what a primordial origin would suggest. The planets in our sample have a wider composition than that of stars, which could indicate formation pathways away from primordial or be the result of random scattering owing to current mass–radius uncertainties as we recover the observed outliers in mock population analysis ∼15% of the time. To truly determine whether the origin is primordial with a 1:1 true relation, we find that sample of at least 150 planets is needed and that stars that are iron enriched or depleted are high-value targets.

We investigate the atomic gas (H i) content of galaxies in groups using early data from the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) All Sky H i survey. Taking advantage of FAST’s blind, wide-area coverage and uniform sensitivity, we assemble a sample of 230 group galaxies belonging to 182 groups at z ≤ 0.03. These groups were identified using a halo-based group finder, and they have a median membership of four galaxies. We also derived a matched control sample of isolated systems, and apply censored-data modeling to include both detections and nondetections. At fixed stellar mass and color, we find that the global median H i fraction of group galaxies differs from that of controls by only −0.04 dex (95% CI [−0.18, 0.16]), indicating at most a mild average offset. The signal is not uniform across populations: satellites are H i poor (median Δf_{H I} = −0.12 dex), whereas centrals are not H i deficient (median Δf_{H I} = 0.13 dex). Group galaxies located within 0.5R₁₈₀ and in denser systems (richness > 10 or local density Σ > 10 gal Mpc⁻²) show stronger negative offsets, whereas galaxies in the outskirts are statistically indistinguishable from the controls. These results refine earlier reports of global group H i deficiency: with deeper blind data and uniform treatment of upper limits, we show that H i depletion is primarily confined to satellites and compact cores rather than being ubiquitous across groups.

Dense cores, the progenitors of stars, are in sub-pc scale and fragmented from pc-scale clumps. However, it is still unclear how strongly the fragmentation process is affected by the properties of the host clumps and how these properties influence the core distribution observed in recent millimeter (mm) and sub-mm observations. To systematically investigate this relation, we employed magnetohydrodynamic (MHD) simulations of convergent flows to generate a large sample of clumps and analyzed their properties using various techniques. Alignment parameters were used to quantify core distribution, while energy terms were calculated to assess the influence of gravity, magnetic fields, and turbulence. We found the core distribution only exhibiting weak correlations between alignment parameters and clump properties. For an individual clump, turbulence is believed to significantly contribute to these features by inducing nonhomologous collapse and ongoing fragmentation. Nevertheless, for the entire population, more compact core distributions are observed due to the dominance of gravity. Overall, these factors suggest that clump properties are not sufficient to accurately determine core distribution.

We investigate how rotating convection responds to the imposition of a latitudinally varying heat flux at the base of the convective layer. This study is motivated by the solar near-surface shear layer, whose flows are thought to transition from a buoyancy-dominated regime near the photosphere to a rotation-dominated regime at depth. Here, we conduct a suite of spherical 3D, nonlinear simulations of rotating convection that operate in either the buoyancy-dominated (high-Rossby-number, high-Ro) or rotation-dominated (low-Rossby-number, low-Ro) regime. At the base of each model convection zone, we impose a heat flux whose latitudinal variation is opposite to the variation that the system would ordinarily develop. In both the low- and high-Ro regimes, a strong thermal wind balance is sustained in the absence of forcing. With a larger flux variation, this balance becomes stronger at high latitudes and weaker at low latitudes. The resulting differential rotation weakens in response, and at sufficiently high forcing, its latitudinal variation reverses for both low- and high-Ro systems. At fixed forcing, there exists a Rossby number above which the convective flows efficiently mix heat laterally, and the imposed flux variation does not imprint to the surface. At sufficiently high Ro, thermal wind balance is no longer satisfied. We discuss these results within the context of the Sun’s near-surface region, which possesses a weakened differential rotation when compared to the deep convection, along with little-to-no variation of photospheric emissivity in latitude.

Theoretical study of the high-order gravity-mode period spacing (ΔP_g) pattern is relevant to a better understanding of the internal properties of intermediate-mass (1.5 M_⊙ < M < 8 M_⊙) main-sequence g-mode pulsators. In this paper, we carry out first-order perturbative analysis to evaluate effects of a sharp, though not discontinuous, transition in the Brunt–Väisälä (BV) frequency on the ΔP_g pattern. Such a finite-width transition in the BV frequency, whose scale height can be comparable to the local wavelength of gravity waves, is expected to develop in relatively low-mass (1.5 M_⊙ < M < 3 M_⊙) main-sequence stars, causing a bump in the second derivative of the BV frequency. Inspired by Unno et al.’s formulation, we treat the bump in the second derivative of the BV frequency as a small perturbation, which allows us to derive an analytical expression for the ΔP_g pattern. The analytical expression shows that the amplitude of the oscillatory ΔP_g pattern is determined by a weighted average of the bump in the second derivative of the BV frequency, where the weighting function is given by the g-mode eigenfunction. Tests with low-mass (∼2 M_⊙) main-sequence stellar models show that the analytical expression can reproduce the numerically computed ΔP_g patterns reasonably well. The results of our perturbative analysis will be useful, for example, in improving semi-analytical expressions for the ΔP_g pattern, thereby enabling investigations of ΔP_g patterns in slowly pulsating B-type stars and γ Dor stars to infer their chemical composition profiles and rotation rates.

Reverberation mapping (RM) is the most promising method to measure the masses of supermassive black holes in the center of active galactic nuclei. However, the dominant jet component hinders the application of the RM method for blazars. In this work, we present a new algorithm to disentangle the contribution of the accretion disk from that of the relativistic jet in blazars by analyzing the spectral break of the optical spectroscopic data. We applied this method to two flat-spectrum radio quasars, PKS 1510−089 and PKS 0736+017. In PKS 1510−089, the variability of the Hγ line is delayed with respect to the disk emission by approximately 94 days, while the Hβ line shows a lag of about 111 days relative to the disk. In PKS 0736+017, the Hγ variability is delayed with respect to the disk by roughly 66 days, and the Hβ line exhibits a lag of about 67 days. Based on these measured time lags, we estimate black hole masses of ∼1.4 × 10⁸M_⊙ for PKS 1510−089 and ∼8.1 × 10⁷M_⊙ for PKS 0736+017. This method paves the way to apply the RM method for blazars and improves the understanding of disk and jet activities.

Close to Earth, the solar wind is usually super-Alfvénic, i.e., the speed of the solar wind is much larger than the Alfvén speed. However, in the lower coronal regions, the solar wind is mostly sub-Alfvénic. With the Parker Solar Probe (PSP) crossing the boundary between the sub- and super-Alfvénic flow, R. Bandyopadhyay et al. performed a turbulence characterization of the sub-Alfvénic solar wind with initial data from encounters 8 and 9. In this study, we reexamine the turbulence properties such as turbulence amplitude, anisotropy of the magnetic field variance, intermittency, and switchback strength using PSP data from encounters 8–19. The later orbits probe lower altitudes and experience sub-Alfvénic conditions more frequently, providing a greater statistical coverage to contrast sub- and super-Alfvénic solar wind. These later orbits also extend the observations from near solar minimum at launch to near solar maximum conditions. Also, by isolating the intervals where the solar wind speed is approximately equal to the Alfvén speed, we explore the transition in more detail. We show that the amplitude of the normalized magnetic field fluctuation is smaller for the sub-Alfvénic samples. While solar wind turbulence in general is shown to be anisotropic, the sub-Alfvénic samples are more anisotropic than the super-Alfvénic samples, in general. Further, we show that the sub- and super-Alfvénic samples do not show much distinction in terms of intermittency strength. Finally, consistent with prior results, we find no evidence for polarity reversing >90° switchbacks in the sub-Alfvénic solar wind.

Previous analytical and numerical investigations of the stochastic properties of field lines in magnetic turbulence have been based on determining the running field-line diffusion coefficient. The latter transport parameter is directly related to the second moment of the field-line distribution function. For the normal diffusive case, this distribution function should be a Gaussian where the width increases linearly with distance. The corresponding transport equation is a usual heat transport or diffusion equation. However, such an equation is no longer valid for nondiffusive cases. In this paper, we systematically develop a theory for obtaining a nondiffusive transport equation. The derived equation has the same structure as a generalized master equation. In the latter equation, we employ a so-called rapid decorrelation approximation to achieve a strong simplification. Its solution is a Gaussian regardless of whether the transport is subdiffusive, normal diffusive, or superdiffusive. For slab turbulence, where the theory of field line random walk is exact, we determine the running diffusion coefficient and the mean squared displacement for a general spectrum in the energy range. The same quantities are then computed by employing numerical simulations. It is demonstrated that the simulations agree perfectly with the analytically obtained distribution functions, and those are indeed Gaussian distributions. The derivations presented in this study can also be used to derive transport equations in other areas of physics such as the theory of energetic particles interacting with magnetohydrodynamic turbulence.

In recent years, multiple Type Ia supernovae (SNe Ia) have been observed with “bumps” in their rising light curves shortly after the explosion. Here, we present SN 2021qvo: an SN Ia that exhibits a clear early bump in photometry obtained by the Young Supernova Experiment. Photometric and spectroscopic observations of SN 2021qvo show that it has a broader light curve, higher peak luminosity, shallower Si iiλ5972 pseudoequivalent width, and lower ejecta velocities than normal SNe Ia, which are all consistent with the characteristics of the 2003fg-like (often called “super-Chandrasekhar”) SN subtype. Including SN 2021qvo, just four known 2003fg-like SNe Ia have sufficient prepeak data to reveal a rising light-curve bump, and all four have bump detections. A host-galaxy analysis reveals that SN 2021qvo exploded in a low-mass galaxy , also consistent with other members of this class. The current leading early bump 2003fg-like SN Ia progenitor model involves an interaction between the circumstellar material (CSM) and the SN ejecta. We test the validity of this theory by modeling the early bump and subsequent light-curve evolution of SN 2021qvo with the Modular Open Source Fitter for Transients. We find that the bump can be modeled with a best-fit CSM mass in the range M_CSM = 3.31−8.51 × 10⁻³M_⊙. SN 2021qvo adds to the small but growing number of 2003fg-like SNe Ia with rising light-curve bumps; as the number of these SNe Ia with CSM estimates continues to grow, population-level inferences about the CSM distribution will be able to constrain the progenitor scenario for these SNe Ia.

Very long baseline interferometry (VLBI) achieves the highest angular resolution in astronomy. VLBI measures corrupted Fourier components, known as visibilities. Reconstructing on-sky images from these visibilities is a challenging inverse problem, particularly for sparse arrays such as the Event Horizon Telescope (EHT) and the Very Long Baseline Array, where incomplete sampling and severe calibration errors introduce significant uncertainty in the image. To help guide convergence and control the uncertainty in image reconstructions, regularization on the space of images is utilized, such as enforcing smoothness or similarity to a fiducial image. Coupled with this regularization is the introduction of a new set of parameters that modulate its strength. We present a hierarchical Bayesian imaging approach (hierarchical interferometric Bayesian Imaging, HIBI) that enables the quantification of uncertainty for all parameters. Incorporating instrumental effects within HIBI is straightforward, allowing for simultaneous imaging and calibration of data. To showcase HIBI’s effectiveness and flexibility, we build a simple imaging model based on Markov random fields and demonstrate how different physical components can be included, e.g., black hole shadow size, and their uncertainties can be inferred. For example, while the original EHT publications were unable to constrain the ring width of M87*, HIBI measures a width of 9.3 ± 1.3 μas. We apply HIBI to image and calibrate EHT synthetic data, real EHT observations of M87*, and multifrequency observations of OJ 287. Across these tests, HIBI accurately recovers a wide variety of image structures and quantifies their uncertainties. HIBI is publicly available in the Comrade VLBI software repository.

Episodic mass accretion is the dominant mechanism for mass assembly in the protostellar phase. Although prior optical time-domain searches have allowed detailed studies of individual outbursts, these searches remain insensitive to the earliest stages of star formation. In this paper, we present the characterization of two FU Orionis (FUor) outbursts identified using the combination of the ground-based, near-infrared Wide-field Infrared Transient Explorer (WINTER) and the space-based, mid-infrared NEOWISE survey. Supplemented with near-infrared spectroscopic follow-up, we show that both objects are bona fide FUor type outbursts based on (i) their proximity to star-forming regions, (ii) large amplitude (2–4 magnitudes) infrared brightening over the last decade, (iii) progenitor colors consistent with embedded (Class I) protostars, and (iv) “mixed-temperature” infrared spectra exhibiting characteristic signatures of cool outer envelopes and a hot inner disk with a wind. While one source, WNTR24-cua, is a known FUor that we independently recover; the second source, WNTR24-egv, is a newly confirmed object. Neither source is detected in contemporaneous ground-based optical imaging, despite flux limits ≳100× fainter than their infrared brightness, demonstrating the capabilities of WINTER to identify heavily obscured young stellar object outbursts. We highlight the capabilities of the Galactic Plane Survey of the recently commissioned WINTER observatory in addressing the poorly understood FUor population with its unique combination of real-time detection capabilities, multicolor sensitivity, weekly cadence, and wide area coverage.

We introduce a simulation-based inference framework to constrain the origins of individual ultra-high-energy cosmic rays by combining realistic three-dimensional propagation modeling with Bayesian parameter estimation. Our method integrates CRPropa 3 simulations, including all relevant interactions and magnetic deflections in both Galactic and extragalactic fields, with approximate Bayesian computation to infer posterior distributions over key parameters such as source position, distance, energy, and magnetic field properties. This approach allows joint constraints from the observed energy and arrival direction to be applied simultaneously, naturally incorporating their correlations in addition to relevant modelling uncertainties. We demonstrate our method by applying it to the Amaterasu particle detected by the TA observatory, the second-highest-energy cosmic ray ever detected. The resulting posterior distributions quantify the regions of space consistent with its reconstructed properties under different energy and composition assumptions, revealing a broader set of nearby source candidates than found in previous analyses. This application highlights the framework’s ability to translate individual ultra-high-energy cosmic-ray observations into directly interpretable source constraints and provides a foundation for future simulation-based analyses of cosmic rays at the highest energies.

We present a systematic study of the evolution of low- and intermediate-mass X-ray binaries consisting of a 1.4 M_⊙ neutron star (NS) and a donor star of mass 1–8 M_⊙. Using grids of detailed MESA simulations, we show that for donor masses of 2–8 M_⊙, mass transfer may be dynamically unstable, leading to a common envelope (CE) phase. By adopting CE ejection efficiencies in the range α_CE = 0.3–3.0, we find that post-CE binaries frequently experience a CE decoupling phase (CEDP), which plays a critical role in determining their final orbital and compositional properties. Systems with initial donor masses ≳3.5 M_⊙ predominantly evolve into NS binaries with carbon–oxygen or oxygen–neon white dwarfs (WDs) with masses between 0.5 and 1.4 M_⊙. Comparison with the observed population of binary pulsars with a WD companion shows better agreement with higher CE ejection efficiencies (α_CE = 3.0). Furthermore, we demonstrate that NSs can accrete a sufficient amount of matter (≳0.01 M_⊙) during the CEDP and subsequent Case BA/BB/BC mass transfer phases to be effectively recycled into millisecond pulsars. We identify two distinct evolutionary channels capable of reproducing the observed characteristics of the millisecond pulsar PSR J1928+1815 with a helium-star companion. Our results highlight the importance of the CEDP in the formation of recycled pulsars and provide constraints on the CE ejection efficiency during binary evolution.

Modeling energy-dependent X-ray pulse profiles from rotation-powered millisecond pulsars observed with Neutron Star Interior and Composition Explorer (NICER) has emerged as a promising avenue for measuring neutron-star radii and probing the equation of state of cold, ultradense matter. However, pulse profile models have often required an unwieldy number of parameters to account for complex surface emission geometries, introducing the risk of overfitting and degeneracies. To explore the number of model parameters that can be inferred uniquely, we perform a quantitative assessment of the information content in X-ray pulse profiles by applying Fourier methods. We determine the number of independent observables that can be reliably extracted from the pulse shapes, as well as from complementary X-ray spectral data obtained with XMM-Newton, for key NICER targets. Our analysis provides a framework for evaluating the match between model complexity and data constraints. It also demonstrates the importance of incorporating in the model the pulsed components of the magnetospheric nonthermal emission, which may often contribute significantly to the observed spectra. Our results highlight limitations in previous inferences of neutron-star radii from NICER observations, which may have incorporated model complexity not supported by the data.

Dense star clusters are thought to contribute significantly to the merger rates of stellar-mass binary black holes (BBHs) detected by the LIGO–Virgo–KAGRA collaboration. We combine N-body dynamic models of realistic dense star clusters with cluster formation histories to estimate the merger rate distribution as a function of primary mass for merging BBHs formed in these environments. It has been argued that dense star clusters—most notably old globular clusters—predominantly produce BBH mergers with primary masses M_p ≈ 30 M_⊙. We show that dense star clusters forming at lower redshifts—and thus having higher metallicities—naturally produce lower-mass BBH mergers. We find that cluster BBH mergers span a wide range of primary mass, from about 6 M_⊙ to above 100 M_⊙, with a peak near 8 M_⊙, reproducing the overall merger rate distribution inferred from gravitational wave detections. Our results show that most low-mass BBH mergers (about 95% with M_p ≲ 20 M_⊙) originate in metal-rich (Z ∼ Z_⊙) dense star clusters, while more massive BBH mergers form predominately in metal-poor globular clusters. We also discuss the role of hierarchical mergers in shaping the BBH mass distribution. Gravitational wave detection of dynamically formed low-mass BBH mergers—potentially identifiable by features such as isotropic spin distributions—may serve as probes of cluster formation histories in metal-rich environments at low redshifts.

We present a spectropolarimetric study of the nearby M4.5V exoplanet host star YZ Cet, based on near-infrared observations obtained with the Spectropolarimètre Infrarouge at the Canada-France-Hawaii Telescope. We detect striking changes in the large-scale magnetic field strength and geometry over the course of just a few stellar rotations, a level of short-term global magnetic field evolution rarely reported in M dwarfs. We modeled the temporal variation of the longitudinal magnetic field using the Gaussian process regression, which allowed us to robustly determine the stellar rotation period and quantify the evolution timescale of the magnetic field. Independent Zeeman Doppler imaging reconstructions of the two epochs confirm a significant reconfiguration of the star’s global magnetic strength and topology. The detection of a weaker complex axisymmetric magnetic field (mean ∣B∣ ∼ 201 G), which changes into a stronger nonaxisymmetric dipole-dominated field (Mean ∣B∣ ∼ 276 G) over a few rotation cycles, is in contrast to results from similar fully convective M dwarf stars. YZ Cet is known to exhibit polarized radio bursts potentially driven by auroral radio emission from star–planet interaction (SPI). By combining our magnetic maps with recent radio observations, we refine the constraints on the magnetic field strength of the innermost planet, YZ Cet b. These results underscore the importance of monitoring stellar magnetic variability to interpret multiwavelength SPI signatures and to characterize the magnetospheres of potentially habitable exoplanets.

During cosmic noon (z ∼ 1–3), when both star formation and black hole growth peaked, galaxy mergers are predicted to trigger dual active galactic nuclei that eventually coalesce as supermassive black hole (SMBH) binaries. However, observations of dual quasars with sub-5 kpc separations—the critical phase preceding final coalescence—have remained challenging due to angular resolution limitations. We present the discovery and confirmation of two subarcsecond dual quasars at z > 1, selected from 59,025 Sloan Digital Sky Survey (SDSS) quasars, which fall within the footprint of the Hyper Suprime-Cam Survey. Using high-resolution Hubble Space Telescope imaging and slitless spectroscopy, we confirmed SDSS J1625+4309 (z = 1.647, separation 055/4.7 kpc) and SDSS J0229−0514 (z = 3.174, separation 042/3.2 kpc), probing the sub-5 kpc separation regime. Through the novel combination of WFC3/IR direct imaging (F140W) and grism spectroscopy (G141), we resolve both components morphologically and spectroscopically confirm their dual nature via detection of Hβ+[O iii] and Mg ii emission lines in each nucleus. Two-dimensional image decomposition reveals distinct host galaxy morphologies: J1625+4309 shows an extended, disturbed structure (R_e = 4.7 kpc) indicative of an ongoing major merger, while J0229−0514 exhibits a compact host (R_e = 1.4 kpc) suggesting an advanced coalescence stage. Black hole mass estimates based on virial relations yield with line-of-sight velocity offsets of (0.7 ± 0.1) × 10³ km s⁻¹ and (1.0 ± 0.2) × 10³ km s⁻¹, respectively. These confirmations directly constrain the frequency and properties of close dual quasars, opening new avenues for studying SMBH mergers at cosmic noon.

We present comprehensive photometric observations and analysis of the totally eclipsing binary CN Tri. The photometric solutions suggest it as an extremely low mass ratio contact binary system with q ∼ 0.08. Multiband photometry obtained using the WH50 and XL85 telescopes, along with high-cadence time-series photometric data from the Transiting Exoplanet Survey Satellite (TESS), reveals that CN Tri is fundamentally a W-type contact binary. However, the light curve morphology from TESS observations exhibits characteristics typical of A-type systems. We successfully reconciled this apparent contradiction through modeling a time-evolving starspot near orbital phase 0.5, which provides a comprehensive explanation for the anomaly observation in this system. This case study demonstrates that starspot-induced light curve distortions can lead to misclassification of contact binary types, offering a valuable framework for interpreting similar anomalies in other W UMa systems with discrepant photometric classifications.

We present new Hubble Space Telescope (HST) imaging of three recently discovered star-forming dwarf galaxies beyond the Local Group: Pavo, Corvus A, and Kamino. The discovery of Kamino is reported here for the first time. They rank among the most isolated faint dwarf galaxies known; hence they provide unique opportunities to study galaxy evolution at the smallest scales, free from the environmental effects of more massive galaxies. Our HST data reach ∼2–4 magnitudes below the tip of the red giant branch (TRGB) for each dwarf, allowing us to measure their distances, structural properties, and recent star formation histories (SFHs). All three galaxies contain a complex stellar population of young and old stars, and are typical of field galaxies in this mass regime (M_V = −10.62 ± 0.08 and Mpc for Pavo, M_V = −10.91 ± 0.10 and D = 3.34 ± 0.11 Mpc for Corvus A, and M_V = −12.02 ± 0.12 and Mpc for Kamino). Our HST-derived SFHs reveal differences among the three dwarfs: Pavo and Kamino show relatively steady, continuous star formation, while Corvus A formed ∼60% of its stellar mass by 10 Gyr ago. These results align with theoretical predictions of diverse evolutionary pathways for isolated low-mass galaxies.

One of the distinctive properties of magnetars, young neutron stars powered mainly by magnetic energy, is the emission of short (≲1 s) bursts of hard X-rays. Such bursts have been observed in nearly all the known magnetars, although at different and time-variable rates of occurrence. In the past two decades, the INTEGRAL satellite has extensively covered the Galactic plane with good imaging capabilities, where most magnetars reside. We present the results of a comprehensive search for magnetar bursts in more than 20 yr of archival data of the INTEGRAL IBIS instrument (15 keV–1 MeV). This led to the detection of 1349 bursts with 30–150 keV fluence in the ∼2 × 10⁻⁹ to 3 × 10⁻⁶ erg cm⁻² range from 21 of the 34 examined magnetars and candidate magnetars with well-known positions. The durations of the bursts, in terms of T₉₀, follow a lognormal distribution centered at ∼0.1 s. Most of the detected bursts originated from three particularly active sources: 1E 1547–5408, SGR 1806–20, and SGR 1935+2154. The integral distributions of their burst fluences follow power laws with slopes β = 0.76±0.04, 0.95±0.06, and 0.92±0.10, respectively. The burst spectra are generally well fit with an exponentially cutoff power law with peak energy E_peak in the range ∼20−60 keV for SGR 1806–20 and SGR 1935+2154, while the bursts of 1E 1547–5408 are slightly harder (E_peak ∼ 35−100 keV). A significant anticorrelation between E_peak and fluence is found for SGR 1806–20, which provided the largest number of bursts among the sources of our sample.

If dark matter is ultra-light and has certain Standard Model interactions, it can change the mass–radius relation of white dwarf (WD) stars. The coherence length of ultra-light dark matter (ULDM) imparts spatial correlations in deviations from the canonical mass–radius relation, and thus, WDs can be used to reconstruct the coherence length, or equivalently the particle mass, of the dark matter field. We simulate the observability of such spatial correlations accounting for realistic complications like variable hydrogen envelope thickness, dust, binaries, measurement noise, and distance uncertainties in DA WDs. Using a machine learning approach on simulated data, we measure the dark matter field coherence length and find that large deviations from the mass–radius relation (∼10% change in radius) are needed to produce an observable signal given realistic noise sources. We apply our spatial correlation measurement routine to the Sloan Digital Sky Survey catalog of 10,207 DA WDs. We detect a positive spatial correlation among WDs at separations corresponding to a coherence length of 300 ± 50 pc, with an average Z-score of 85 for WDs separated by less than this coherence length. We conclude that this signal is due to observational bias. The signal can be explained by an offset between measurements and theory for nearby cool WDs, and the presence of few, low-temperature WDs with noisy measurements at farther distances. With future improvements in WD models and measurement techniques, particularly for cool WDs, this method can provide interesting constraints on ULDM models.

We use microlensing to probe the inner broad line region (BLR) of the lensed quasar SDSS J1004+4112, finding evidence of substructure. We study the recurrent microlensing events observed in the blue wing of the C IV emission line in image A of this lensed quasar from a series of 20 spectra taken over 15 yr. We obtain a microlensing light curve and confirm the presence of three high magnification events (Δm > –0.7 mag). A caustic crossing is a natural explanation for each one of the events. The fast rising and fading of the events imply that the width of the region scanned by the caustic in each event, ≲0.1 μas (≲0.93 ± 0.36 light days), is much smaller than the BLR size. However, the large range of velocities involved implies significant overlapping with the inner BLR velocity field. An elongated thin substructure in the BLR fulfills both requirements at once. A sequence of caustics crossing a single elongated substructure may be a possible explanation of the observed recurrence. However, this hypothesis requires some ad hoc assumptions about the microlens population. Alternatively, a single caustic encountering several narrow-stripped or bow-shaped substructures in the approaching part of the BLR could explain the variability. We discuss the possible identification of these elongated substructures with ripples or spiral structure on the inner BLR. Simulations of caustic crossings of a rippled disk statistically support this interpretation. The study of the C IV emission-line variability in SDSS J1004+4112 illustrates the incomparable scanning power of microlensing in both velocity and space.

Isotopes of chromium (Cr) and other iron-group elements are predominantly made in the inner shells of supernovae and are later reprocessed via the slow neutron capture process (s-process) in asymptotic giant branch (AGB) stars. Nucleosynthetic models of low-mass, solar metallicity AGB stars yield significant overproduction of ⁵⁴Cr (δ⁵⁴Cr values ∼ +160‰) with limited variations in other Cr isotopes, relative to solar system values. Here we report Cr, C, and N isotopic compositions of 16 individual presolar silicon carbide (SiC) grains of the KJG series (1.5–3 μm) from the Murchison (CM2.0) meteorite. ¹²C/¹³C and ¹⁴N/¹⁵N ratios of the 14 mainstream SiC grains range from 29 to 108 and 259 to 7800, respectively. These C, N isotopic compositions are consistent with their formation in red giant and AGB stars. Two types of AB grains could have originated in a J-type C-star (AB2) and a type-II supernova (AB). The majority of mainstream grains display close-to-solar Cr isotopic compositions, indicating the Cr was not significantly processed within their parent AGB stars. A mainstream SiC grain with relatively high ⁵⁴Cr enrichment of δ⁵⁴Cr ∼ 700‰ likely originated from a very low metallicity parent star based on the stellar nucleosynthesis model (FRUITY). We consider the plausible origin of this grain from Galactic halo stars, migration from the outer Galactic disk, and other scenarios. Elemental Cr concentrations of the grains vary from ∼1 to 9 ppm, with 75% of the grains displaying an average concentration of ∼2 ppm. Cr concentration does not vary significantly with grain size, suggesting that the Cr in the SiC grains condensed during grain formation and was not implanted at a later stage.

Synchrotron radiation detected from relativistic astrophysical objects such as pulsar-wind nebulae and jets from active galactic nuclei depends on the magnetic fields and the distribution functions of energetic electrons in these systems. Relativistic magnetically dominated turbulence has been recognized as an efficient mechanism for structure formation and nonthermal particle acceleration in these environments. Recent numerical simulations of relativistic turbulence have provided insights into the energy distribution functions of accelerated electrons. Much less is currently understood about their pitch angle distributions, which are crucial for accurately interpreting the spectra of synchrotron radiation. We perform a detailed case study of the pitch angle distributions formed during the process of turbulent acceleration for B₀/δB₀ = 10 and , where B₀ is the uniform component of the magnetic field, δB₀ is the fluctuating component, and is the plasma magnetization based on the magnetic fluctuations. We find that even minimal numerical noise can cause substantial pitch angle scattering, but we demonstrate techniques for overcoming the numerical challenges associated with the evolution of very small pitch angles. Our numerical results are consistent with the phenomenological considerations found in C. Vega et al. (2024a, 2025).

Theoretical models have long predicted the existence of shocks in multitransonic accretion flows onto a black hole, yet their fate under general relativistic simulations has not been fully tested. In this study, we present results from high-resolution two-dimensional general relativistic hydrodynamic and general relativistic magnetohydrodynamic simulations of low angular momentum accretion flows onto Kerr black holes, focusing on the formation of shocks in transonic accretion flow. We demonstrate that for specific combinations of energy and angular momentum, global shock solutions naturally emerge between multiple sonic points. These shocks are sustained in both corotating and counterrotating cases, and their locations depend on specific energy, angular momentum, and the spin of the black hole, which is in good agreement with analytical solutions. In magnetized flows, weak magnetic fields preserve the shock structure, whereas strong fields suppress it, enhancing turbulence and driving powerful, magnetically dominated jets/outflows. The strength and structure of the outflow also depend on a black hole spin and magnetization, with higher black hole spin parameters leading to faster jets. Shock solutions are found only in super-Alfvénic regions, where kinetic forces dominate. Our findings provide important insights into the physics of hot corona formation and jet launching in low angular momentum accretion systems such as Sgr A* (weak jet/outflow) and X-ray binaries.

We investigate the impact of the Bondi–Hoyle–Lyttleton (BHL) accretion mechanism on the evolution of nova eruptions in symbiotic systems by systematically varying three key input parameters: the initial donor (asymptotic giant branch, AGB) mass, the initial white dwarf (WD) mass, and the initial binary separation (a). We explore models with AGB masses in the range 1.5–3.5 M_⊙, WD masses in the range 0.7–1.25 M_⊙, and separations in the range 1000–8000 R_⊙. We find all our models to show a significant, long-term orbital increase. This trend is primarily driven by the fact that ∼99% of the AGB’s mass is lost from the system, either directly via wind—that is never accreted onto the WD—or accreted onto the WD and then ejected during nova eruptions. This results in the effect of the mass loss (or transfer) on the orbit dominating over the effect of the angular momentum loss sinks that could shrink the orbit, leading to a consistent orbit widening. Consequently, all of our WD masses gradually decrease. A more massive WD achieves a higher mass transfer efficiency and accretion rate, meaning a slightly better mass retention efficiency per nova. However, since a higher accretion rate causes more frequent eruptions, the total WD mass loss over the AGB lifetime is more substantial. We conclude that symbiotic systems transferring mass via the BHL mechanism are unlikely to be Type Ia supernova progenitors.

The historical reconstruction of the Sun’s surface magnetic field remains a persistent challenge, limiting our ability to investigate the long-term global properties of the Sun, including the evolution of the large-scale magnetic field, solar cycle prediction, reconstruction of total solar irradiance, and secular solar variability. In this study, we employ the Advective Flux Transport (AFT) model in conjunction with our newly developed Synthetic Active Region Generator (SARG) to construct a catalog of synthetic active regions (ARs) spanning solar cycles 1–24 (1755–2020). We use the SIDC/SILSO sunspot number version 2.0 as the sole input governing the properties of the synthetic ARs in this catalog. This SARG catalog is then incorporated into the AFT model, which simulates the emergence of new ARs on the Sun, which are then transported under the influence of surface flows to produce maps of the full-Sun radial photospheric magnetic field over the entire 265 yr period. We modulate the AR tilt for each cycle in order to ensure that the polar fields are consistent with the solar cycle amplitudes. We find that the polar fields derived from these simulations exhibit excellent correlation (r > 0.8) with observational proxies, including polar faculae counts and Ca ii K polar network indices. Daily synchronic maps from these simulations for the entire 265 yr period are made publicly available to support a wide range of applications beyond those presented in this work.

We present a comprehensive analysis of the relationship between galaxies and the intergalactic medium (IGM) during the late stages of cosmic reionization, based on the complete JWST EIGER dataset. Using deep NIRCam 3.5 μm slitless spectroscopy, we construct a sample of 948 [O iii]λ5008-emitting galaxies with −21.4 ≲ M_UV ≲ −17.2 spanning 5.33 < z < 6.97 along six quasar sight lines. We correlate these galaxies with Lyα and Lyβ transmission measured from high-resolution quasar spectra across multiple redshift intervals. We find clear redshift evolution in the correlation between galaxy density and transmission: it is suppressed in overdense regions at z < 5.50, while enhanced at 5.70 < z < 6.15. The intermediate range exhibits a transitional behavior. Cross-correlation measurements further reveal excess absorption within ∼8 cMpc of galaxies at low redshifts, and enhanced transmission at intermediate scales (∼5–20 cMpc) at z > 5.70. Statistical tests using mock catalogs with realistic galaxy clustering but no correlation with the transmission field confirm that the observed correlations are unlikely to arise by chance. The evolving signals can be explained by stronger absorption in overdense regions, combined with the competing influences of local radiation fields and the rising background radiation. While local radiation dominates ionization of the surrounding IGM at earlier times, the background becomes increasingly important, eventually surpassing the impact of nearby galaxies. These results support an inside-out progression of reionization, with ionized regions originating around clustered, star-forming galaxies and gradually extending into underdense regions.

2MASS J04381486+2611399 (or J0438) is one of the few young brown dwarfs (BDs) with a highly inclined (i ∼ 70°) disk. Here we report results from JWST Mid-Infrared Instrument (MIRI) Medium Resolution Spectroscopy, Hubble Space Telescope (HST) Advanced Camera for Surveys, and Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 observations. Despite its late spectral type (M7.25), the spectrum of J0438 resembles those of inner disks around earlier-type stars (K1–M5, T Tauri stars), with a volatile reservoir lacking hydrocarbons (except for acetylene, C₂H₂) and dominated by water. Other identified species are H₂, CO₂, HCN, [Ar⁺], and [Ne⁺]. The dominance of water over hydrocarbons is driven by multiple factors such as disk dynamics, young disk age, low accretion rate, and possible inner disk clearing. J0438 appears highly dynamic, showing a seesaw-like variability and extended emission in H₂S(1), S(3), S(5), [Ne⁺], and CO (J = 3–2). Interestingly, the CO emission reaches up to 400 au from the BD, suggesting ongoing infalling/outflowing activity impacting the disk chemistry. These observations underscore the combined power of MIRI, HST, and ALMA in characterizing the chemical diversity and dynamics of BD disks.

S. D. von Fellenberg et al. reported the first mid-infrared detection of a flare from Sgr A*. The JWST/MIRI/Medium Resolution Spectrometer observations were consistent with an orbiting hotspot undergoing electron injection with a spectrum that subsequently breaks from synchrotron cooling. However, mid-infrared extinction measurements appropriate for these data were not yet determined, and, therefore, the temporal evolution of the absolute spectral index remained unknown. This work applies new Sgr A* extinction measurements to the flare observations. The evolution of the spectral index after the peak is fully consistent with that reported in Paper I with a maximum absolute mid-infrared spectral index α_MIR = 0.45 ± 0.01_stat ± 0.08_sys during the second mid-infrared flare peak, matching the known near-infrared spectral index during bright states (α_NIR ≈ 0.5). There was a near-instantaneous change in the mid-infrared spectral index of Δα_MIR = 0.33 ± 0.06_stat ± 0.11_sys at the flare onset. We propose this as a quantitative definition for this infrared flare’s beginning, physically interpreted as the underlying electron distribution’s transition into a hard power-law distribution. This paper also reports the Submillimeter Array millimeter polarization during the flare, which shows a small, distorted, but overall CW-oriented Stokes Q–U loop during the third mid-infrared peak. Extrapolating the mid-infrared flux power law to the millimeter yields a variable flux consistent with the observed 220 GHz emission. These results, together with the Paper I modeling, plausibly suggest a single hotspot produced both the mid-infrared and millimeter variability during this event. However, additional flares are required to make a general statement about the millimeter and mid-infrared connection.

We present here the results from a second epoch of phase-referenced VLBA observations of eight Seyfert and LINER galaxies from the KISSR sample. These sources were chosen based on the presence of double peaks or asymmetries in their emission lines as observed in SDSS spectra. Parsec-scale radio emission is detected in seven of the eight sources in the second epoch. Jet-like features appear to persist over a ∼4–9 yr timeline in these “radio-quiet” AGN. A few sources like KISSR1494, however, show significantly different structures after a 9 yr interval. KISSR102, which was previously suggested to be a binary black hole candidate based on the presence of two compact cores, shows the tentative signatures of superluminal jet motion (1.05 ± 0.45c). Tentative superluminal motion in a jet knot has been reported in another source, KISSR872 (1.65 ± 0.57c). We present 1.5 GHz images from the VLA A-array of four sources. These images reveal core-lobe or core-halo structures. The alignment of the VLBI jet direction with the kiloparsec-scale spectral index gradient, as well as the mismatch between the star formation rate derived from the radio and Hα line emission, support the suggestion that the kiloparsec-scale emission is AGN-jet-related. The jets in KISSR sources appear to lose collimation over spatial scales between 200 pc and 1 kpc. Overall, the characteristics of the KISSR jets are reminiscent of similar properties observed in VLBI monitoring studies of “radio-loud” AGN jets even as subtle differences related to the compactness and brightness of jet features remain.

The Compton Spectrometer and Imager (COSI) is a Compton telescope designed to survey the 0.2–5 MeV sky, consisting of a compact array of cross-strip germanium detectors. It is planned to be launched in 2027 into an equatorial low-Earth (530 km) orbit with a prime mission duration of 2 yr. The observation of MeV gamma rays is dominated by background. Thus, background simulation and identification are crucial for predicting the sensitivities of instruments. In this work we perform Monte Carlo simulations of the background for the first 3 months in orbit, and we extrapolate the results to 2 yr in orbit in order to determine the buildup of the activation due to long-lived isotopes. The simulations account for the known background components and include time-dependent rate variations due to the geomagnetic cutoff and South Atlantic Anomaly (SAA) passages. In addition, they include detailed modeling of the delayed activation due to short- and long-lived isotopes. We determine the rates of events induced by the background that are reconstructed as Compton events in the simulated COSI data. We find that the extragalactic background photons dominate at low energies (<660 keV), while delayed activation from cosmic-ray primaries (proton/alpha) and albedo photons dominate at higher energies. As part of this work, a comparison at low latitude (∣b∣ ≤ 1°) between recent measurement of the SAA and the AP9/AE9 model has been made, showing an overestimation of the flux by a factor ∼9 by the model. The systematic uncertainties associated with these components are quantified.