Table of contents for issue 2, volume 932, The Astrophysical Journal

Visible light observations from the Wide-field Imager for Solar PRobe (WISPR) aboard the Parker Solar Probe (PSP) mission offer a unique opportunity to study the dust environment near the Sun. The existence of a dust-free zone (DFZ) around stars was postulated almost a century ago. Despite numerous attempts to detect it from as close as 0.3 au, observational evidence of a circumsolar DFZ has remained elusive. Analysis of WISPR images obtained from heliocentric distances between 13.3–53.7 R_⊙ over multiple PSP orbits shows a gradually decreasing brightness gradient along the symmetry axis of the F-corona for coronal heights between 19 and 9 R_⊙. Below 9 R_⊙, the gradient reverses its trend, approaching the radial dependence exhibited at heights above 19 R_⊙. After taking into account the effects of both the electron corona background and the nonresolved starlight, the WISPR observations down to 4 R_⊙ are consistent with forward-modeling simulations of the F-corona brightness within [−6, 5]% if a circumsolar region of depleted dust density between 19 and 5 R_⊙ enclosing a DFZ is considered. In addition, we show, for the first time, that the F-corona brightness inward of about 15 R_⊙ depends on the observer’s location for observing distances below 35 R_⊙.

We present a new investigation of the intergalactic medium near reionization using dark gaps in the Lyβ forest. With its lower optical depth, Lyβ offers a potentially more sensitive probe to any remaining neutral gas compared to the commonly used Lyα line. We identify dark gaps in the Lyβ forest using spectra of 42 QSOs at z_em > 5.5, including new data from the XQR-30 VLT Large Programme. Approximately 40% of these QSO spectra exhibit dark gaps longer than 10 h⁻¹ Mpc at z ≃ 5.8. By comparing the results to predictions from simulations, we find that the data are broadly consistent both with models where fluctuations in the Lyα forest are caused solely by ionizing ultraviolet background fluctuations and with models that include large neutral hydrogen patches at z < 6 due to a late end to reionization. Of particular interest is a very long (L = 28 h⁻¹ Mpc) and dark (τ_eff ≳ 6) gap persisting down to z ≃ 5.5 in the Lyβ forest of the z = 5.85 QSO PSO J025−11. This gap may support late reionization models with a volume-weighted average neutral hydrogen fraction of 〈x_{H I}〉 ≳ 5% by z = 5.6. Finally, we infer constraints on 〈x_{H I}〉 over 5.5 ≲ z ≲ 6.0 based on the observed Lyβ dark gap length distribution and a conservative relationship between gap length and neutral fraction derived from simulations. We find 〈x_{H I}〉 ≤ 0.05, 0.17, and 0.29 at z ≃ 5.55, 5.75, and 5.95, respectively. These constraints are consistent with models where reionization ends significantly later than z = 6.

We present an ALMA-Herschel joint analysis of sources detected by the ALMA Lensing Cluster Survey (ALCS) at 1.15 mm. Herschel/PACS and SPIRE data at 100–500 μm are deblended for 180 ALMA sources in 33 lensing cluster fields that are detected either securely (141 sources; in our main sample) or tentatively at S/N ≥ 4 with cross-matched HST/Spitzer counterparts, down to a delensed 1.15 mm flux density of ∼0.02 mJy. We performed far-infrared spectral energy distribution modeling and derived the physical properties of dusty star formation for 125 sources (109 independently) that are detected at >2σ in at least one Herschel band. A total of 27 secure ALCS sources are not detected in any Herschel bands, including 17 optical/near-IR-dark sources that likely reside at z = 4.2 ± 1.2. The 16th, 50th, and 84th percentiles of the redshift distribution are 1.15, 2.08, and 3.59, respectively, for ALCS sources in the main sample, suggesting an increasing fraction of z ≃ 1 − 2 galaxies among fainter millimeter sources (f₁₁₅₀ ∼ 0.1 mJy). With a median lensing magnification factor of , ALCS sources in the main sample exhibit a median intrinsic star formation rate of M_⊙ yr⁻¹, lower than that of conventional submillimeter galaxies at similar redshifts by a factor of ∼3. Our study suggests weak or no redshift evolution of dust temperature with L_IR < 10¹²L_⊙ galaxies within our sample at z ≃ 0 − 2. At L_IR > 10¹²L_⊙, the dust temperatures show no evolution across z ≃ 1–4 while being lower than those in the local universe. For the highest-redshift source in our sample (z = 6.07), we can rule out an extreme dust temperature (>80 K) that was reported for MACS0416 Y1 at z = 8.31.

Recent ground- and space-based observations show that stars with multiple planets are common in the Galaxy. Most of these observational methods are biased toward detecting large planets near to their host stars. Because of these observational biases, these systems can hide small, close-in planets or far-orbiting (big or small) companions. These planets can still exert dynamical influence on known planets and have such influence exerted on them in turn. In certain configurations, this influence can destabilize the system; in others, the star’s gravitational influence can instead further stabilize the system. For example, in systems with planets close to the host star, effects arising from general relativity can help to stabilize the configuration. We derive criteria for hidden planets orbiting both beyond and within known planets that quantify how strongly general relativistic effects can stabilize systems that would otherwise be unstable. As a proof of concept, we investigate the several planets in a system based on Kepler-56 and show that the outermost planet will not disrupt the system even at high eccentricities, and we show that an Earth-radius planet could be stable within this system if it orbits below 0.08 au. Furthermore, we provide specific predictions to known observed systems by constraining the parameter space of possible hidden planets.

DI Cha A is K0-type pre-main-sequence star, the brightest component of a quadruple stellar system. Here we report on a detailed study of this star based on archival VLTI/MIDI and VLTI/PIONIER infrared interferometric observations, as well as optical-infrared photometric monitoring from ground-based and space-born instruments. We determined the structure of the circumstellar disk by fitting simultaneously the interferometric visibilities and the spectral energy distribution, using both analytical models and the radiative transfer code RADMC-3D. The modeling revealed that the radial density distribution of the disk appears to have a gap between 0.21 and 3.0 au. The inner ring, whose inner size coincides with the sublimation radius, is devoid of small, submicrometer-sized dust grains. The inner edge of the outer disk features a puffed-up rim, typically seen in intermediate-mass stars. Grain growth, although less progressed, was also detected in the outer disk. The inner ring is variable at mid-infrared wavelengths on both daily and annual timescales, while the star stays remarkably constant in the optical, pointing to geometrical or accretion changes in the disk as possible explanations for the flux variations.

The joint detection of gravitational waves and the gamma-ray counterpart of a binary neutron star merger event, GW170817, unambiguously validates the connection between short gamma-ray bursts and compact binary object (CBO) mergers. We focus on a special scenario where short gamma-ray bursts produced by CBO mergers are embedded in disks of active galactic nuclei (AGNs), and we investigate the γ-ray emission produced in the internal dissipation region via synchrotron, synchrotron self-Compton, and external inverse Compton (EIC) processes. In this scenario, isotropic thermal photons from the AGN disks contribute to the EIC component. We show that a low-density cavity can be formed in the migration traps, leading to the embedded mergers producing successful GRB jets. We find that the EIC component would dominate the GeV emission for typical CBO mergers with an isotropic-equivalent luminosity of L_j,iso = 10^48.5 erg s⁻¹ that are located close to the central supermassive black hole. Considering a long-lasting jet of duration T_dur ∼ 10²–10³ s, we find that the future Cherenkov Telescope Array (CTA) will be able to detect its 25–100 GeV emission out to a redshift z = 1.0. In the optimistic case, it is possible to detect the on-axis extended emission simultaneously with GWs within one decade using MAGIC, H.E.S.S., VERITAS, CTA, and LHAASO-WCDA. Early diagnosis of prompt emissions with Fermi-GBM and HAWC can provide valuable directional information for the follow-up observations.

The search for extraterrestrial intelligence at radio frequencies has largely been focused on continuous-wave narrowband signals. We demonstrate that broadband pulsed beacons are energetically efficient compared to narrowband beacons over longer operational timescales. Here, we report the first extensive survey searching for such broadband pulsed beacons toward 1883 stars as a part of the Breakthrough Listen’s search for advanced intelligent life. We conducted 233 hr of deep observations across 4–8 GHz using the Robert C. Byrd Green Bank Telescope and searched for three different classes of signals with artificial (or negative) dispersion. We report a detailed search—leveraging a convolutional neural network classifier on high-performance GPUs—deployed for the very first time in a large-scale search for signals from extraterrestrial intelligence. Due to the absence of any signal-of-interest from our survey, we place a constraint on the existence of broadband pulsed beacons in our solar neighborhood: ≲1 in 1000 stars have transmitter power densities ≳10⁵ W Hz⁻¹ repeating ≤500 s at these frequencies.

Rocky bodies of the inner solar system display a systematic depletion of “moderately volatile elements” (MVEs) that correlates with the expected condensation temperature of their likely host materials under protoplanetary nebula conditions. In this paper, we present and test a new hypothesis in which open-system loss processes irreversibly remove vaporized MVEs from high nebula altitudes, leaving behind the more refractory solids residing much closer to the midplane. The MVEs irreversibly lost from the nebula through these open-system loss processes are then simply unavailable for condensation onto planetesimals forming even much later, after the nebula has cooled, overcoming a critical difficulty encountered by previous models of this type. We model open-system loss processes operating at high nebula altitudes, such as resulting from disk winds flowing out of the system entirely, or layered accretion directly onto the young Sun. We find that mass-loss rates higher than those found in typical T-Tauri disk winds, lasting short periods of time, are most satisfactory, pointing to multiple intense early outburst stages. Using our global nebula model, incorporating realistic particle growth and inward drift for solids, we constrain how much the MVE-depletion signature in the inner region is diluted by the drift of undepleted material from the outer nebula. We also find that a significant irreversible loss of the common rock-forming elements (Fe, Mg, Si) can occur, leading to a new explanation of another long-standing puzzle of the apparent “enhancement” in the relative abundance of highly refractory elements in chondrites.

We report on the study of six Chandra observations (four epochs) of the Central Compact Object (CCO) in the Cassiopeia A supernova remnant with the ACIS instrument in the subarray mode. This mode minimizes spectrum-distorting instrumental effects such as pileup. The data were taken over a time span of ∼14 yr. If a non-magnetic carbon atmosphere is assumed for this youngest known CCO, then the temperature change is constrained to be K yr⁻¹ or K yr⁻¹ (1σ uncertainties) for constant or varying absorbing hydrogen column density. These values correspond to cooling rates of −1.5% ± 0.3% per 10 yr and −2.3% ± 0.4% per 10 yr, respectively. We discuss an apparent increase in the cooling rate in the last five years and the variations of the inferred absorbing hydrogen column densities between epochs. Considered together, these changes could indicate systematic effects such as caused by, e.g., an imperfect calibration of the increasing contamination of the ACIS filter.

Progenitor models for the “luminous” subclass of Fast Blue Optical Transients (LFBOTs; prototype: AT2018cow) are challenged to simultaneously explain all of their observed properties: fast optical rise times of days or less; peak luminosities ≳10⁴⁴ erg s⁻¹; low yields ≲0.1M_⊙ of ⁵⁶Ni; aspherical ejecta with a wide velocity range (≲3000 km s⁻¹ to ≳0.1–0.5c with increasing polar latitude); presence of hydrogen-depleted-but-not-free dense circumstellar material (CSM) on radial scales from ∼10¹⁴ cm to ∼3 × 10¹⁶ cm; embedded variable source of non-thermal X-ray/γ-rays, suggestive of a compact object. We show that all of these properties are consistent with the tidal disruption and hyper-accretion of a Wolf-Rayet (WR) star by a black hole or neutron star binary companion. In contrast with related previous models, the merger occurs with a long delay (≳100 yr) following the common envelope (CE) event responsible for birthing the binary, as a result of gradual angular momentum loss to a relic circumbinary disk. Disk-wind outflows from the merger-generated accretion flow generate the ⁵⁶Ni-poor aspherical ejecta with the requisite velocity range. The optical light curve is powered primarily by reprocessing X-rays from the inner accretion flow/jet, though CSM shock interaction also contributes. Primary CSM sources include WR mass loss from the earliest stages of the merger (≲10¹⁴ cm) and the relic CE disk and its photoevaporation-driven wind (≳10¹⁶ cm). Longer delayed mergers may instead give rise to supernovae Type Ibn/Icn (depending on the WR evolutionary state), connecting these transient classes with LFBOTs.

We present a detailed study of the Planck-selected binary galaxy cluster PLCK G165.7+67.0 (G165; z = 0.348). A multiband photometric catalog is generated incorporating new imaging from the Large Binocular Telescope/Large Binocular Camera and Spitzer/IRAC to existing imaging. To cope with the different image characteristics, robust methods are applied in the extraction of the matched-aperture photometry. Photometric redshifts are estimated for 143 galaxies in the 4 arcmin² field of overlap covered by these data. We confirm that strong-lensing effects yield 30 images of 11 background galaxies, of which we contribute new photometric redshift estimates for three image multiplicities. These constraints enable the construction of a revised lens model with a total mass of M_{600 kpc} = (2.36 ± 0.23) × 10¹⁴M_⊙. In parallel, new spectroscopy using MMT/Binospec and archival data contributes thirteen galaxies that meet our velocity and transverse radius criteria for cluster membership. The two cluster components have a pair-wise velocity of ≲100 km s⁻¹, favoring an orientation in the plane of the sky with a transverse velocity of 100–1700 km s⁻¹. At the same time, the brightest cluster galaxy (BCG) is offset in velocity from the systemic mean value, suggesting dynamical disturbance. New LOFAR and Very Large Array data uncover head-tail radio galaxies in the BCG and a large red galaxy in the northeast component. From the orientation and alignment of the four radio trails, we infer that the two cluster components have already traversed each other, and are now exiting the cluster.

Thermal electrons cannot directly participate in the process of diffusive acceleration at electron–ion shocks because their Larmor radii are smaller than the shock transition width: this is the well-known electron injection problem of diffusive shock acceleration. Instead, an efficient pre-acceleration process must exist that scatters electrons off of electromagnetic fluctuations on scales much shorter than the ion gyroradius. The recently found intermediate-scale instability provides a natural way to produce such fluctuations in parallel shocks. The instability drives comoving (with the upstream plasma) ion–cyclotron waves at the shock front and only operates when the drift speed is smaller than half of the electron Alfvén speed. Here we perform particle-in-cell simulations with the SHARP code to study the impact of this instability on electron acceleration at parallel nonrelativistic, electron–ion shocks. To this end, we compare a shock simulation in which the intermediate-scale instability is expected to grow to simulations where it is suppressed. In particular, the simulation with an Alfvénic Mach number large enough to quench the intermediate instability shows a great reduction (by two orders of magnitude) of the electron acceleration efficiency. Moreover, the simulation with a reduced ion-to-electron mass ratio (where the intermediate instability is also suppressed) not only artificially precludes electron acceleration but also results in erroneous electron and ion heating in the downstream and shock transition regions. This finding opens up a promising route for a plasma physical understanding of diffusive shock acceleration of electrons, which necessarily requires realistic mass ratios in simulations of collisionless electron–ion shocks.

Spectral hardening has been identified in solar flare hard X-ray observations for several decades and remains a puzzle. We examine spectral hardening under the diffusive shock acceleration mechanism using numerical simulations. The hardening is related to the finite width of the shock and is controlled by the shock Péclet number. We implement two different types of Monte Carlo simulations. The first is based on the backward stochastic differential equation method, where the Parker transport equation is solved by casting it to a set of stochastic different equations, and by following the trajectories of individual quasiparticles. In the second approach, we follow real particles and particles are assumed to move freely between scatterings from magnetic turbulence in the plasma. The scattering is modeled as either large-angle hard-sphere elastic collision, or small-angle pitch-angle scattering. We show that the results from these two approaches agree well with each other and agree with analytical results. We also use a Pan-spectrum form to fit the resulting spectra.

We present an analytic model for clustered supernovae (SNe) feedback in galaxy disks, incorporating the dynamical evolution of superbubbles formed from spatially overlapping SNe remnants. We propose two realistic outcomes for the evolution of superbubbles in galactic disks: (1) the expansion velocity of the shock front falls below the turbulent velocity dispersion of the interstellar medium in the galaxy disk, whereupon the superbubble stalls and fragments, depositing its momentum entirely within the galaxy disk; or (2) the superbubble grows in size to reach the gas scale height, breaking out of the galaxy disk and driving galactic outflows/fountains. In either case, we find that superbubble breakup/breakout almost always occurs before the last Type II SN (≲40 Myr) in the recently formed star cluster, assuming a standard high-end initial mass function slope, and scalings between stellar lifetimes and masses. The threshold between these two cases implies a break in the effective strength of feedback in driving turbulence within galaxies, and a resulting change in the scalings of, for example, star formation rates with gas surface density (the Kennicutt–Schmidt relation) and the star formation efficiency in galaxy disks.

We report the results of X-ray (Chandra X-ray Observatory (CXO)) and radio (ATCA) observations of the pulsar wind nebula (PWN) powered by the young pulsar PSR J1016–5857, which we dub “the Goose” PWN. In both bands, the images reveal a tail-like PWN morphology that can be attributed to the pulsar’s motion. By comparing archival and new CXO observations, we measure the pulsar’s proper motion μ = 28.8 ± 7.3 mas yr⁻¹, yielding a projected pulsar velocity v ≈ 440 ± 110 km s⁻¹ (at d = 3.2 kpc); its direction is consistent with the PWN shape. Radio emission from the PWN is polarized, with the magnetic field oriented along the pulsar tail. The radio tail connects to a larger radio structure (not seen in X-rays), which we interpret as a relic PWN (also known as a plerion). The spectral analysis of the CXO data shows that the PWN spectrum softens from Γ = 1.7 to Γ ≈ 2.3–2.5 with increasing distance from the pulsar. The softening can be attributed to the rapid synchrotron burn-off, which would explain the lack of X-ray emission from the older relic PWN. In addition to nonthermal PWN emission, we detected thermal emission from a hot plasma, which we attribute to the host supernova remnant. The radio PWN morphology and the proper motion of the pulsar suggest that the reverse shock passed through the pulsar’s vicinity and pushed the PWN to one side.

Accretion of interplanetary dust onto gas giant exoplanets is considered. Poynting–Robertson drag causes dust particles from distant reservoirs to slowly inspiral toward the star. Orbital simulations for the three-body system of the star, planet, and dust particle show that a significant fraction of the dust may accrete onto massive planets in close orbits. The deceleration of the supersonic dust in the planet’s atmosphere is modeled, including ablation by thermal evaporation and sputtering. The fraction of the accreted dust mass deposited as gas-phase atoms is found to be large for close-in orbits and massive planets. If mass outflow and vertical mixing are sufficiently weak, the accreted dust produces a constant mixing ratio of atoms and remnant dust grains below the stopping layer. When vertical mixing is included along with settling, the solutions interpolate between the mixing ratio due to the meteoric source above the homopause, and that of the well-mixed deeper atmosphere below the homopause. The line opacity from atoms and continuum opacity from remnant dust may be observable in transmission spectra for sufficiently large dust accretion rates, a grain size distribution tilted toward the blowout size, and sufficiently weak vertical mixing. If mixing is strong, the meteoric source may still act to augment heavy elements mixed up from the deep atmosphere as well as provide nucleation sites for the formation of larger particles. The possible role of the Lorentz drag force in limiting the flow speeds and mixing coefficient for pressures ≲1 mbar is discussed.

Under the right conditions, brown dwarfs that gain enough mass late in their lives to cross the hydrogen-burning limit will not turn into low-mass stars, but rather remain essentially brown dwarf–like. While these objects, called either beige dwarfs or overmassive brown dwarfs, may exist in principle, it remains unclear exactly how they would form astrophysically. We show that accretion from AGB winds, aided by the wind Roche lobe overflow mechanism, is likely to produce a substantial population of observable overmassive brown dwarfs, though other mechanisms are still plausible. Specifically, we predict that Sun-like stars born with a massive brown dwarf companion on an orbit with a semimajor axis of order 10 au will likely produce overmassive brown dwarfs, which may be found today as companions to the donor star's remnant white dwarf. The identification and characterization of such an object would produce unique constraints on binary evolution, because there is a solid upper limit on the brown dwarf's initial mass.

The X8.2-class limb flare on 2017 September 10 is among the best studied solar flare events owing to its great similarity to the standard flare model and the broad coverage by multiple spacecraft and ground-based observations. These multiwavelength observations indicate that electron acceleration and transport are efficient in the reconnection and flare looptop regions. However, there lacks a comprehensive model for explaining and interpreting the multi-faceted observations. In this work, we model the electron acceleration and transport in the early impulsive phase of this flare. We solve the Parker transport equation that includes the primary acceleration mechanism during magnetic reconnection in the large-scale flare region modeled by MHD simulations. We find that electrons are accelerated up to several MeV and fill a large volume of the reconnection region, similar to the observations shown in microwaves. The electron spatial distribution and spectral shape in the looptop region agree well with those derived from the microwave and hard X-ray emissions before magnetic islands grow large and dominate the acceleration. Future emission modelings using the electron maps will enable direct comparison with microwave and hard X-ray observations. These results shed new light on the electron acceleration and transport in a broad region of solar flares within a data-constrained realistic flare geometry.

The central strong activities in core-collapse supernovae are expected to produce the overturning of the Fe- and Si/O-rich ejecta during the supernova explosion based on multidimensional simulations. X-ray observations of the supernova remnant Cassiopeia A have indicated that the Fe-rich ejecta lies outside the Si-rich materials in the southeastern region, which is consistent with the hypothesis on the inversion of the ejecta. We investigate the kinematic and nucleosynthetic properties of the inverted ejecta layers in detail to understand its formation process using the data taken by the Chandra X-Ray Observatory. Three-dimensional velocities of Fe- and Si/O-rich ejecta are obtained as >4500 km s⁻¹ and ∼2000–3000 km s⁻¹, respectively, by combining proper motion and line-of-sight velocities, indicating that the velocity of the Si/O-rich ejecta is slower than that of the Fe-rich ejecta from the early stages of the explosion. To constrain their burning regime, the Cr/Fe mass ratios are evaluated as % in the outermost Fe-rich region and % in the inner Fe/Si-rich region, suggesting that the complete Si burning layer is invertedly located to the incomplete Si burning layer. All the results support the ejecta overturning at the early stages of the remnant’s evolution or during the supernova explosion of Cassiopeia A.

Solar flares may be the best-known examples of the explosive conversion of magnetic energy into bulk motion, plasma heating, and particle acceleration via magnetic reconnection. The energy source for all flares is the highly sheared magnetic field of a filament channel above a polarity inversion line (PIL). During the flare, this shear field becomes the so-called reconnection guide field (i.e., the nonreconnecting component), which has been shown to play a major role in determining key properties of the reconnection, including the efficiency of particle acceleration. We present new high-resolution, three-dimensional, magnetohydrodynamics simulations that reveal the detailed evolution of the magnetic shear/guide field throughout an eruptive flare. The magnetic shear evolves in three distinct phases: shear first builds up in a narrow region about the PIL, then expands outward to form a thin vertical current sheet, and finally is transferred by flare reconnection into an arcade of sheared flare loops and an erupting flux rope. We demonstrate how the guide field may be inferred from observations of the sheared flare loops. Our results indicate that initially the guide field is larger by about a factor of 5 than the reconnecting component, but it weakens by more than an order of magnitude over the course of the flare. Instantaneously, the guide field also varies spatially over a similar range along the three-dimensional current sheet. We discuss the implications of the remarkable variability of the guide field for the timing and localization of efficient particle acceleration in flares.

We report on high-resolution observations of recurrent fan-like jets by the Goode Solar Telescope in multiple wavelengths inside a sunspot group. The dynamics behavior of the jets is derived from the Hα line profiles. Quantitative values for one well-identified event have been obtained, showing a maximum projected velocity of 42 km s⁻¹ and a Doppler shift of the order of 20 km s⁻¹. The footpoints/roots of the jets have a lifted center on the Hα line profile compared to the quiet Sun, suggesting a long-lasting heating at these locations. The magnetic field between the small sunspots in the group shows a very high resolution pattern with parasitic polarities along the intergranular lanes accompanied by high-velocity converging flows (4 km s⁻¹) in the photosphere. Magnetic cancellations between the opposite polarities are observed in the vicinity of the footpoints of the jets. Along the intergranular lanes horizontal magnetic field around 1000 G is generated impulsively. Overall, all the kinetic features at the different layers through the photosphere and chromosphere favor a convection-driven reconnection scenario for the recurrent fan-like jets and evidence a site of reconnection between the photosphere and chromosphere corresponding to the intergranular lanes.

We present a self-consistent model of the Milky Way to reproduce the observed distributions (spectral type, absolute J-band magnitude, effective temperature) and total velocity dispersion of brown dwarfs. For our model, we adopt parametric forms for the star formation history and initial-mass function, published evolutionary models, and theoretical age–velocity relations. Using standard Markov Chain Monte Carlo methods, we derive a power-law index of the initial-mass function of α = −0.71 ± 0.11, which is an improvement over previous studies. We consider a gamma-function form for the star formation history, though we find that this complex model is only slightly favored over a declining exponential. We find that a velocity variance that linearly increases with age and has an initial value of km s⁻¹ best reproduces the total velocity dispersions. Given the similarities to main-sequence stars, this suggests brown dwarfs likely form via similar processes, but we recognize that the sizable uncertainties on σ₀ preclude firm conclusions. To further refine these conclusions, we suggest that wide-field infrared imaging or low-resolution spectroscopic surveys, such as with the Nancy Grace Roman Space Telescope or Euclid, could provide large samples of brown dwarfs with robust spectral types that could probe the thickness of the thin disk. In this way, the number counts and population demographics could probe the same physical processes as with the kinematic measurements, however may provide larger samples and be subject to different selection biases.

State transitions in black hole X-ray binaries are likely caused by gas evaporation from a thin accretion disk into a hot corona. We present a height-integrated version of this process, which is suitable for analytical and numerical studies. With radius r scaled to Schwarzschild units and coronal mass accretion rate to Eddington units, the results of the model are independent of black hole mass. State transitions should thus be similar in X-ray binaries and an active galactic nucleus. The corona solution consists of two power-law segments separated at a break radius r_b ∼ 10³(α/0.3)⁻², where α is the viscosity parameter. Gas evaporates from the disk to the corona for r > r_b, and condenses back for r < r_b. At r_b, reaches its maximum, . If at r ≫ r_b the thin disk accretes with , then the disk evaporates fully before reaching r_b, giving the hard state. Otherwise, the disk survives at all radii, giving the thermal state. While the basic model considers only bremsstrahlung cooling and viscous heating, we also discuss a more realistic model that includes Compton cooling and direct coronal heating by energy transport from the disk. Solutions are again independent of black hole mass, and r_b remains unchanged. This model predicts strong coronal winds for r > r_b, and a T ∼ 5 × 10⁸ K Compton-cooled corona for r < r_b. Two-temperature effects are ignored, but may be important at small radii.

We present a multiband study of FRB 20180916B, a repeating source with a 16.3 day periodicity. We report the detection of four, one, and seven bursts from observations spanning 3 days using the upgraded Giant Metrewave Radio Telescope (300–500 MHz), the Canadian Hydrogen Intensity Mapping Experiment (400–800 MHz) and the Green Bank Telescope (600–1000 MHz), respectively. We report the first ever detection of the source in the 800–1000 MHz range along with one of the widest instantaneous bandwidth detections (200 MHz) at lower frequencies. We identify 30 μs wide structures in one of the bursts at 800 MHz, making it the lowest frequency detection of such structures for this fast radio burst thus far. There is also a clear indication of high activity of the source at a higher frequency during earlier phases of the activity cycle. We identify a gradual decrease in the rotation measure over two years and no significant variations in the dispersion measure. We derive useful conclusions about progenitor scenarios, energy distribution, emission mechanisms, and variation of the downward drift rate of emission with frequency. Our results reinforce that multiband observations are an effective approach to study repeaters, and even one-off events, to better understand their varying activity and spectral anomalies.

Inference is crucial in modern astronomical research, where hidden astrophysical features and patterns are often estimated from indirect and noisy measurements. Inferring the posterior of hidden features, conditioned on the observed measurements, is essential for understanding the uncertainty of results and downstream scientific interpretations. Traditional approaches for posterior estimation include sampling-based methods and variational inference (VI). However, sampling-based methods are typically slow for high-dimensional inverse problems, while VI often lacks estimation accuracy. In this paper, we propose α-deep probabilistic inference, a deep learning framework that first learns an approximate posterior using α-divergence VI paired with a generative neural network, and then produces more accurate posterior samples through importance reweighting of the network samples. It inherits strengths from both sampling and VI methods: it is fast, accurate, and more scalable to high-dimensional problems than conventional sampling-based approaches. We apply our approach to two high-impact astronomical inference problems using real data: exoplanet astrometry and black hole feature extraction.

We present a beam pattern measurement of the Canadian Hydrogen Intensity Mapping Experiment (CHIME) made using the Sun as a calibration source. As CHIME is a pure drift-scan instrument, we rely on the seasonal north–south motion of the Sun to probe the beam at different elevations. This semiannual range in elevation, combined with the radio brightness of the Sun, enables a beam measurement that spans ∼7200 square degrees on the sky without the need to move the telescope. We take advantage of observations made near solar minimum to minimize the impact of solar variability, which is observed to be <10% in intensity over the observation period. The resulting data set is highly complementary to other CHIME beam measurements—both in terms of angular coverage and systematics—and plays an important role in the ongoing program to characterize the CHIME primary beam.

Methanol (CH₃OH) is an abundant interstellar species and is known to be an important precursor of various interstellar complex organic molecules. Among the methanol isotopologues, CH₂DOH is one of the most abundant isotopologues and it is often used to study the deuterium fractionation of CH₃OH in interstellar medium. However, the emission lines of CH₂DOH can sometimes be optically thick, making the derivation of its abundance unreliable. Therefore, observations of its presumably optically thin ¹³C substituted species, ¹³CH₂DOH, are essential to overcome this issue. In this study, the rotational transitions of ¹³CH₂DOH have been measured in the millimeter-wave region from 216 GHz to 264 GHz with an emission-type millimeter- and submillimeter-wave spectrometer by using a deuterium and ¹³C enriched sample. The frequency accuracy of measured ¹³CH₂DOH is less than a few kHz, and the relative line intensity error is less than 10% in most of the frequency range by taking advantage of the wide simultaneous frequency-coverage of the emission-type spectrometer. These results offer a good opportunity to detect ¹³CH₂DOH in space, which will allow us to study the deuterium fractionation of CH₃OH in various sources through accurate determination of the CH₂DOH abundance.

The Fisher information matrix (FM) plays an important role in forecasts and inferences in many areas of physics. While giving fast parameter estimation with Gaussian likelihood approximation in the parameter space, the FM can only give the ellipsoidal posterior contours of the parameters and it loses the higher-order information beyond Gaussianity. We extend the FM in gravitational-wave (GW) data analysis by using the Derivative Approximation for LIkelihoods (DALI), a method to expand the likelihood, while keeping it positive definite and normalizable at every order, for more accurate forecasts and inferences. When applied to two real GW events, GW150914 and GW170817, DALI can reduce the difference between the FM approximation and the real posterior by 5 times in the best case. The calculation times of DALI and the FM are at the same order of magnitude, while obtaining the real full posterior will take several orders of magnitude longer. Besides more accurate approximations, higher-order correction from DALI provides a fast assessment of the FM analysis and gives suggestions for complex sampling techniques that are computationally intensive. We recommend using the DALI method as an extension to the FM method in GW data analysis to pursue better accuracy while still keeping the speed.

The stellar initial mass function (IMF) is a fundamental property in the measurement of stellar masses and galaxy star formation histories. In this work, we focus on the most massive galaxies in the nearby universe . We obtain high-quality Magellan/LDSS-3 long-slit spectroscopy with a wide wavelength coverage of 0.4–1.01 μm for 41 early-type galaxies (ETGs) in the MASSIVE survey and derive high signal-to-noise spectra within an aperture of R_e/8. Using detailed stellar synthesis models, we constrain the elemental abundances and stellar IMF of each galaxy through full spectral modeling. All the ETGs in our sample have an IMF that is steeper than a Milky Way (Kroupa) IMF. The best-fit IMF mismatch parameter, α_IMF = (M/L)/(M/L)_MW, ranges from 1.1 to 3.1, with an average of 〈α_IMF〉 = 1.84, suggesting that on average, the IMF is more bottom heavy than Salpeter. Comparing the estimated stellar masses with the dynamical masses, we find that most galaxies have stellar masses that are smaller than their dynamical masses within the 1σ uncertainty. We complement our sample with lower-mass galaxies from the literature and confirm that is positively correlated with , , and . From the combined sample, we show that the IMF in the centers of more massive ETGs is more bottom heavy. In addition, we find that is positively correlated with both [Mg/Fe] and the estimated total metallicity [Z/H]. We find suggestive evidence that the effective stellar surface density Σ_Kroupa might be responsible for the variation of α_IMF. We conclude that σ, [Mg/Fe], and [Z/H] are the primary drivers of the global stellar IMF variation.

We use 13 yr of Swift/BAT observations to probe the nature and origin of the hard X-ray (14–195 KeV) emission in Centaurus A. Since the beginning of the Swift operation in 2004, significant X-ray variability in the 14–195 KeV band has been detected, with mild changes in the source spectrum. Spectral variations became more eminent after 2013, following a softer-when-brighter trend. Using the power spectral density (PSD) method, we find that the observed hard X-ray photon flux variations are consistent with a red-noise process of slope, −1.3, with no evidence for a break in the PSD. We find a significant correlation between the hard X-ray and 230 GHz radio flux variations, with no time delay longer than 30 days. The temporal and spectral analysis confirms that the X-ray emission generated by the accretion in the ADAF model is sub-dominant as compared with the emission arising from that produced by the inner regions of the radio jet.

Recently, many different pulsar timing array (PTA) collaborations have reported strong evidence for a common stochastic process in their data sets. The reported amplitudes are in tension with previously computed upper limits. In this paper, we investigate how using a subset of a set of pulsars biases Bayesian upper limit recovery. We generate 500 simulated PTA data sets, based on the NANOGrav 11 yr data set with an injected stochastic gravitational-wave background (GWB). We then compute the upper limits by sampling the individual pulsar likelihoods, and combine them through a factorized version of the PTA likelihood to obtain upper limits on the GWB amplitude, using different numbers of pulsars. We find that it is possible to recover an upper limit (95% credible interval) below the injected value, and that it is significantly more likely for this to occur when using a subset of pulsars to compute the upper limit. When picking pulsars to induce the maximum possible bias, we find that the 95% Bayesian upper limit recovered is below the injected value in 10.6% of the realizations (53 of 500). Further, we find that if we choose a subset of pulsars in order to obtain a lower upper limit than when using the full set of pulsars, the distribution of the upper limits obtained from these 500 realizations is shifted to lower-amplitude values.

We have performed phase-resolved spectral analysis of the accreting pulsar 1A 0535+262 based on observations of Insight-HXMT during the 2020 type II outburst of the source. We focus on the two-dimensional dependence of the cyclotron resonance scattering features (CRSFs) along the outburst time and at different phases. The fundamental CRSF line (f-CRSF) shows different time- and phase-dependent behaviors. At higher luminosity, the phase profile of the f-CRSF energy changes from a single peak to double peaks, with the transition occurring at MJD 59185. On the contrary, the first harmonic CRSF (first CRSF) at ∼100 keV is only detected within a narrow phase range (0.8−1.0) accompanied by a shallow f-CRSF line. Based on these results, we speculate that when the source enters the supercritical regime, the higher accretion column height can significantly enhance the harmonic line at a narrow phase through an “anti-pencil” beam at a higher energy band. At the same time, it will also affect the behavior of the fundamental line.

We employ self-supervised representation learning to distill information from 76 million galaxy images from the Dark Energy Spectroscopic Instrument Legacy Imaging Surveys’ Data Release 9. Targeting the identification of new strong gravitational lens candidates, we first create a rapid similarity search tool to discover new strong lenses given only a single labeled example. We then show how training a simple linear classifier on the self-supervised representations, requiring only a few minutes on a CPU, can automatically classify strong lenses with great efficiency. We present 1192 new strong lens candidates that we identified through a brief visual identification campaign and release an interactive web-based similarity search tool and the top network predictions to facilitate crowd-sourcing rapid discovery of additional strong gravitational lenses and other rare objects: github.com/georgestein/ssl-legacysurvey.

The outflow of an object traveling in a fluid can shape the fluid morphology by forming a forward bow shock that accelerates the object via gravitational feedback. This dynamical effect, namely, dynamical antifriction, has been studied in idealized infinite uniform media, which suffers from the convergence problem due to the long-range nature of gravitation. In this work, we conduct global 3D hydrodynamic simulations to study this effect in the scenario of a binary system, where the collision of outflows from both stars creates a suitable configuration. We demonstrate with simulations that a dense and slow outflow can give rise to a positive torque on the binary and lead to the expansion of the orbit. As an application, we show that binaries consisting of an AGB star and an outflowing pulsar can experience ∼10% orbital expansion during the AGB stage, in addition to the contribution from mass loss. We also prove that the gravitational force drops as O(r⁻³) from the center of mass in the binary scenarios, which guarantees a quick converge of the overall effect.

The next generation of large ground- and space-based optical telescopes will have segmented primary mirrors. Co-phasing the segments requires a sensitive wavefront sensor capable of measuring phase discontinuities. The Zernike wavefront sensor (ZWFS) is a passive wavefront sensor that has been demonstrated to sense segmented-mirror piston, tip, and tilt with picometer precision in laboratory settings. We present the first on-sky results of an adaptive optics fed ZWFS on a segmented aperture telescope, W.M. Keck Observatory's Keck II. Within the Keck Planet Imager and Characterizer light path, the ZWFS mask operates in the H band using an InGaAs detector (CRED2). We piston segments of the primary mirror by a known amount and measure the mirror's shape using both the ZWFS and a phase retrieval method on data acquired with the facility infrared imager, NIRC2. In the latter case, we employ slightly defocused NIRC2 images and a modified Gerchberg–Saxton phase retrieval algorithm to estimate the applied wavefront error. We find good agreement when comparing the phase retrieval and ZWFS reconstructions, with average measurements of 408 ± 23 and 394 ± 46 nm, respectively, for three segments pistoned by 400 nm of optical path difference (OPD). Applying various OPDs, we find that we are limited to ∼100 nm OPD of applied piston, due to insufficient averaging of the adaptive optics residuals of our observations. We also present simulations of the ZWFS that help to explain the systematic offset observed in the ZWFS reconstructed data.

Coronal magnetic fields are well known to be one of the crucial parameters defining coronal physics and space weather. However, measuring the global coronal magnetic fields remains challenging. The polarization properties of coronal radio emissions are sensitive to coronal magnetic fields. While they can prove to be useful probes of coronal and heliospheric magnetic fields, their usage has been limited by technical and algorithmic challenges. We present a robust algorithm for precise polarization calibration and imaging of low-radio frequency solar observations and demonstrate it on data from the Murchison Widefield Array, a Square Kilometre Array (SKA) precursor. This algorithm is based on the Measurement Equation framework, which forms the basis of all modern radio interferometric calibration and imaging. It delivers high-dynamic-range and high-fidelity full-Stokes solar radio images with instrumental polarization leakages <1%, on par with general astronomical radio imaging, and represents the state of the art. Opening up this rewarding, yet unexplored, phase space will enable multiple novel science investigations and offer considerable discovery potential. Examples include detection of low-level circular polarization from thermal coronal emission to estimate large-scale quiescent coronal fields; polarization of faint gyrosynchrotron emissions from coronal mass ejections for robust estimation of plasma parameters; and detection of the first-ever linear polarization at these frequencies. This method has been developed with the SKA in mind and will enable a new era of high-fidelity spectropolarimetric snapshot solar imaging at low radio frequencies.

We explore the evolution of the X-ray luminosity function of quasars and the intrinsic correlation between the X-ray and 2500 Å ultraviolet luminosities, utilizing techniques verified in previous works and a sample of over 4000 quasars detected with Chandra and XMM-Newton in the range 0 < z < 5. We find that quasars have undergone significantly less evolution with redshift in their total X-ray luminosity than in other wave bands. We then determine that the best-fit intrinsic power-law correlation between the X-ray and ultraviolet luminosities, of the form , is γ = 0.28 ± 0.03, and we derive the luminosity function and density evolution in the X-ray band. We discuss the implications of these results for models of quasar systems.

We present a spectrum of the diffuse Galactic light (DGL) between 3700 and 10,000 Å, obtained by correlating optical sky intensity with far-infrared dust emission. We use nearly 250,000 blank-sky spectra from BOSS/SDSS-III together with IRIS-reprocessed maps from the IRAS satellite. The larger sample size compared to SDSS-II results in a factor-of-2 increase in signal to noise. We combine these data sets with a model for the optical/far-infrared correlation that accounts for self-absorption by dust. The spectral features of the DGL agree remarkably well with the features present in stellar spectra. There is evidence for a difference in the DGL continuum between the regions covered by BOSS in the northern and southern Galactic hemispheres. We interpret the difference at red wavelengths as the result of a difference in stellar populations, with mainly old stars in both regions, but a higher fraction of young stars in the south. There is also a broad excess in the southern DGL spectrum over the prediction of a simple radiative transfer model, without a clear counterpart in the north. We interpret this excess, centered at ∼6500 Å, as evidence for luminescence in the form of extended red emission. The observed strength of the 4000 Å break indicates that at most ∼7% of the dust-correlated light at 4000 Å can be due to blue luminescence. Our DGL spectrum provides constraints on dust scattering and luminescence, independent of measurements of extinction.

The variability of the X-ray emission from active galactic nuclei is often characterized using time lags observed between soft and hard energy bands in the detector. The time lags are usually computed using the complex cross-spectrum, which is based on the Fourier transforms of the hard and soft time series data. It has been noted that some active galactic nuclei display soft X-ray time lags, in addition to the more ubiquitous hard lags. Hard time lags are thought to be produced via propagating fluctuations, spatial reverberation, or via the thermal Comptonization of soft seed photons injected into a hot electron cloud. The physical origin of the soft lags has been a subject of debate over the last decade. Currently, the reverberation interpretation is recognized as a leading theory. In this paper, we explore the alternative possibility that the soft X-ray time lags result partially from the thermal and bulk Comptonization of monochromatic seed photons which, in the case of the narrow-line Seyfert 1 galaxy 1H 0707-495, may correlate with fluorescence of iron L-line emission. In our model, the seed photons are injected into a hot, quasi-spherical corona in the inner region of the accretion flow. We develop an exact, time-dependent analytical model for the thermal and bulk Comptonization of the seed photons based on a Fourier-transformed radiation transport equation, and we demonstrate that the model successfully reproduces both the hard and soft time lags observed from 1H 0707-495.

High spatial resolution CO observations of midinclination (≈30°–75°) protoplanetary disks offer an opportunity to study the vertical distribution of CO emission and temperature. The asymmetry of line emission relative to the disk major axis allows for a direct mapping of the emission height above the midplane, and for optically thick, spatially resolved emission in LTE, the intensity is a measure of the local gas temperature. Our analysis of Atacama Large Millimeter/submillimeter Array archival data yields CO emission surfaces, dynamically constrained stellar host masses, and disk atmosphere gas temperatures for the disks around the following: HD 142666, MY Lup, V4046 Sgr, HD 100546, GW Lup, WaOph 6, DoAr 25, Sz 91, CI Tau, and DM Tau. These sources span a wide range in stellar masses (0.50–2.10 M_⊙), ages (∼0.3–23 Myr), and CO gas radial emission extents (≈200–1000 au). This sample nearly triples the number of disks with mapped emission surfaces and confirms the wide diversity in line emitting heights (z/r ≈ 0.1 to ≳0.5) hinted at in previous studies. We compute the radial and vertical CO gas temperature distributions for each disk. A few disks show local temperature dips or enhancements, some of which correspond to dust substructures or the proposed locations of embedded planets. Several emission surfaces also show vertical substructures, which all align with rings and gaps in the millimeter dust. Combining our sample with literature sources, we find that CO line emitting heights weakly decline with stellar mass and gas temperature, which, despite large scatter, is consistent with simple scaling relations. We also observe a correlation between CO emission height and disk size, which is due to the flared structure of disks. Overall, CO emission surfaces trace ≈2–5× gas pressure scale heights (H_g) and could potentially be calibrated as empirical tracers of H_g.

We explore the use of observed polar coronal holes (CHs) to constrain the flux distribution within the polar regions of global solar magnetic field maps in the absence of reliable quality polar field observations. Global magnetic maps, generated by the Air Force Data Assimilative Photospheric flux Transport (ADAPT) model, are modified to enforce field unipolarity thresholds both within and outside observed CH boundaries. The polar modified and unmodified maps are used to drive Wang–Sheeley–Arge (WSA) models of the corona and solar wind (SW). The WSA-predicted CHs are compared with the observations, and SW predictions at the WIND and Ulysses spacecraft are also used to provide context for the new polar modified maps. We find that modifications of the polar flux never worsen and typically improve both the CH and SW predictions. We also confirm the importance of the choice of the domain over which WSA generates the coronal magnetic field solution but find that solutions optimized for one location in the heliosphere can worsen predictions at other locations. Finally, we investigate the importance of low-latitude (i.e., active region) magnetic fields in setting the boundary of polar CHs, determining that they have at least as much impact as the polar fields themselves.

Observations of the extragalactic (z = 0.0141) transient AT 2018cow established a new class of energetic explosions shocking a dense medium, producing luminous emission at millimeter and submillimeter wavelengths. Here we present detailed millimeter- through centimeter-wave observations of a similar transient, ZTF 20acigmel (AT 2020xnd), at z = 0.2433. Using observations from the NOrthern Extended Millimeter Array and the Very Large Array, we model the unusual millimeter and radio emission from AT 2020xnd under several different assumptions and ultimately favor synchrotron radiation from a thermal electron population (relativistic Maxwellian). The thermal electron model implies a fast but subrelativistic (v ≈ 0.3c) shock and a high ambient density (n_e ≈ 4 × 10³ cm⁻³) at Δt ≈ 40 days. The X-ray luminosity of L_X ≈ 10⁴³ erg s⁻¹ exceeds simple predictions from the radio and UVOIR luminosity and likely has a separate physical origin, such as a central engine. Using the fact that month-long luminous (L_ν ≈ 2 × 10³⁰ erg s⁻¹ Hz⁻¹ at 100 GHz) millimeter emission appears to be a generic feature of transients with fast (t_1/2 ≈ 3 days) and luminous (M_peak ≈ −21 mag) optical light curves, we estimate the rate at which transients like AT 2018cow and AT 2020xnd will be detected by future wide-field millimeter transient surveys such as CMB-S4 and conclude that energetic explosions in dense environments may represent a significant population of extragalactic transients in the 100 GHz sky.

We present the first direct measurement of the proper motion of pulsar J1124–5916 in the young, oxygen-rich supernova remnant G292.0+1.8. Using deep Chandra ACIS-I observations from 2006 to 2016, we measure a positional change of 021 ± 005 over the ∼10 yr baseline, or ∼002 yr⁻¹. At a distance of 6.2 ± 0.9 kpc, this corresponds to a kick velocity in the plane of the sky of 612 ± 152 km s⁻¹. We compare this direct measurement against the velocity inferred from estimates based on the center of mass of the ejecta. Additionally, we use this new proper-motion measurement to compare the motion of the neutron star to the center of expansion of the optically emitting ejecta. We derive an age estimate for the supernova remnant of ≳2000 yr. The high measured kick velocity is in line with recent studies of high proper motion neutron stars in other Galactic supernova remnants and consistent with a hydrodynamic origin to the neutron star kick.

Periodic variables illuminate the physical processes of stars throughout their lifetime. Wide-field surveys continue to increase our discovery rates of periodic variable stars. Automated approaches are essential to identify interesting periodic variable stars for multiwavelength and spectroscopic follow-up. Here we present a novel unsupervised machine-learning approach to hunt for anomalous periodic variables using phase-folded light curves presented in the Zwicky Transient Facility Catalogue of Periodic Variable Stars by Chen et al. We use a convolutional variational autoencoder to learn a low-dimensional latent representation, and we search for anomalies within this latent dimension via an isolation forest. We identify anomalies with irregular variability. Most of the top anomalies are likely highly variable red giants or asymptotic giant branch stars concentrated in the Milky Way galactic disk; a fraction of the identified anomalies are more consistent with young stellar objects. Detailed spectroscopic follow-up observations are encouraged to reveal the nature of these anomalies.

We propose a novel mechanism where primordial black hole (PBH) dark matter is formed much later in the history of the universe, between the epochs of Big Bang nucleosynthesis and cosmic microwave background photon decoupling. In our setup, one does not need to modify the scale-invariant inflationary power spectra; instead, a late-phase transition in a strongly interacting fermion–scalar fluid (which occurs naturally around redshift 10⁶ ≤ z_T ≤ 10⁸) creates an instability in the density perturbation as the sound speed turns imaginary. As a result, the dark matter perturbation grows exponentially in sub-Compton scales. This follows the immediate formation of an early dense dark matter halo, which finally evolves into PBHs due to cooling through scalar radiation. We calculate the variance of the density perturbations and the PBH fractional abundances f(M) by using a nonmonochromatic mass function. We find that the peak of our PBH mass function lies between 10⁻¹⁶ and 10⁻¹⁴ solar mass for z_T ≃ 10⁶, and thus that it can constitute the entire dark matter of the universe. In PBH formation, one would expect a temporary phase where an attractive scalar balances the Fermi pressure. We numerically confirm that such a state indeed exists, and we find the radius and density profile of the temporary static structure of the dark matter halo, which finally evolves into PBHs due to cooling through scalar radiation.

HESS J1843–033 is a very high energy gamma-ray source whose origin remains unidentified. This work presents, for the first time, the energy spectrum of gamma rays beyond 100 TeV from the HESS J1843–033 region using the data recorded by the Tibet air shower array and its underground muon detector array. A gamma-ray source with an extension of 034 ± 012 is successfully detected above 25 TeV at (α, δ) = (28109 ± 010, −376 ± 009) near HESS J1843–033 with a statistical significance of 6.2σ, and the source is named TASG J1844–038. The position of TASG J1844–038 is consistent with those of HESS J1843–033, eHWC J1842–035, and LHAASO J1843–0338. The measured gamma-ray energy spectrum in 25 TeV < E < 130 TeV is described with (E/40 TeV)^{−3.26±0.30} TeV⁻¹ cm⁻² s⁻¹, and the spectral fit to the combined spectra of HESS J1843–033, LHAASO J1843–0338, and TASG J1844–038 implies the existence of a cutoff at 49.5 ± 9.0 TeV. Associations of TASG J1844–038 with SNR G28.6–0.1 and PSR J1844–0346 are also discussed in detail for the first time.

The evolution of the dark energy (DE) density is a crucial quantity for understanding the nature of DE. Often, the quantity is described by the so-called equation of state; that is, the ratio of the DE pressure to its density. In this scenario, the DE density is always positive throughout cosmic history, and a negative value is not allowed. Assuming a homogeneous and isotropic universe, we reconstruct the DE density directly from observational data and investigate its evolution throughout cosmic history. We consider the latest Type Ia supernova, baryon acoustic oscillation, and cosmic chronometer data, and reconstruct the DE density in both flat and nonflat universes up to redshift z ∼ 3. The results are well in agreement with ΛCDM up to redshift z ∼ 1.5, but we see a weak sign of negative DE density at high redshifts.

TMC-1A is a protostellar source harboring a young protostar, IRAS 04365+2353, and shows highly asymmetric features of a few 100 au scale in its molecular emission lines. Blueshifted emission is much stronger in the CS (J = 5–4) line than redshifted emission. This asymmetry can be explained if the gas accretion is episodic and takes the form of cloudlet capture, given that the cloudlet is approaching toward us. The gravity of the protostar transforms the cloudlet into a stream and changes its velocity along the flow. The emission from the cloudlet should be blueshifted before the periastron, while it should be redshifted after the periastron. If a major part of cloudlet has not reached the periastron, the former should be dominant. We perform hydrodynamical simulations to examine the validity of the scenario. Our numerical simulations can reproduce the observed asymmetry if the orbit of the cloudlet is inclined to the disk plane. The inclination can explain the slow infall velocity observed in the C¹⁸O (J = 2–1) line emission. Such episodic accretion may occur in various protostellar cores since actual clouds could have inhomogeneous density distributions. We also discuss the implication of the cloudlet capture on observations of related objects.

Thermochemical equilibrium is one of the most commonly used assumptions in current exoplanet retrievals. As science operations with the James Webb Space Telescope (JWST) draw near and with the planned launch of Ariel, it is crucial to assess the underlying biases and assumptions made when applying self-consistent chemistry to spectral retrievals. Here we use the flexibility of TauREx 3.1 to cross-compare three state-of-the-art chemical equilibrium codes: ACE, FastChem, and GGchem. We simulate JWST spectra for ACE, FastChem, GGchem, and GGchem+condensation containing only the elements C, H, O, and N and spectra for FastChem, GGchem, and GGchem+condensation with a more extensive range of elements, giving seven simulated JWST spectra in total, and then cross-retrieve, giving a total of 56 retrievals. Our analysis demonstrates that, like-for-like, all chemical codes retrieve the correct parameters to within 1% of the truth. However, in retrievals, where the contained elements do not match the truth, parameters such as metallicity deviate by 20% while maintaining extremely low uncertainties <1%, giving false confidence. This point is of major importance for future analyses on JWST and Ariel, highlighting that self-consistent chemical schemes that do not employ the proper assumptions (missing species, fixed elemental ratios, condensation) are at risk of confidently biasing interpretations. Free chemistry retrievals employing parametric descriptions of the chemical profiles can provide alternative unbiased explorations.

We present recent updates and improvements of the graphical processing unit (GPU) N-body code GENGA. Modern state-of-the-art simulations of planet formation require the use of a very high number of particles to accurately resolve planetary growth and to quantify the effect of dynamical friction. At present the practical upper limit is in the range of 30,000–60,000 fully interactive particles; possibly a little more on the latest GPU devices. While the original hybrid symplectic integration method has difficulties to scale up to these numbers, we have improved the integration method by (i) introducing higher level changeover functions and (ii) code improvements to better use the most recent GPU hardware efficiently for such large simulations. We added treatments of non-Newtonian forces such as general relativity, tidal interaction, rotational deformation, the Yarkovsky effect, and Poynting–Robertson drag, as well as a new model to treat virtual collisions of small bodies in the solar system. We added new tools to GENGA, such as semi-active test particles that feel more massive bodies but not each other, a more accurate collision handling and a real-time openGL visualization. We present example simulations, including a 1.5 billion year terrestrial planet formation simulation that initially started with 65,536 particles, a 3.5 billion year simulation without gas giants starting with 32,768 particles, the evolution of asteroid fragments in the solar system, and the planetesimal accretion of a growing Jupiter simulation. GENGA runs on modern NVIDIA and AMD GPUs.

Supernovae emit large fluxes of neutrinos, which can be detected by detectors on Earth. Future multi-kiloton scale detectors will be sensitive to several neutrino interaction channels, with thousands of events expected if a supernova emerges in the galaxy neighborhood. There are a limited number of tools to study the interaction rates of supernova neutrinos, although a plethora of available supernova models exist. EstrellaNueva is an open-source software to calculate expected rates of supernova neutrinos in detectors using target materials with typical compositions, and additional compositions can be easily added. This software considers the flavor transformation of neutrinos in the supernova through the adiabatic Mikheyev–Smirnov–Wolfenstein effect, and their interaction in detectors through several channels. Most of the interaction cross sections, such as neutrino–electron and neutrino–proton elastic scattering, inverse beta decay, and coherent elastic neutrino–nucleus scattering, have been analytically implemented. This software provides a link between supernova simulations and the expected events in detectors by calculating fluences and event rates in order to ease any comparison between theory and observation. It provides a simple and standalone tool to explore many physics scenarios, offering an option to add analytical cross sections and define any target material.

Planetary systems are thought to be born in protoplanetary disks. Isotope ratios are a powerful tool for investigating the material origin and evolution from molecular clouds to planetary systems via protoplanetary disks. However, it is challenging to measure the isotope (isotopologue) ratios, especially in protoplanetary disks, because the emission lines of major species are saturated. We developed a new method to overcome these challenges by using optically thin line wings induced by thermal broadening. As a first application of the method, we analyzed two carbon monoxide isotopologue lines, ¹²CO 3–2 and ¹³CO 3–2, from archival observations of a protoplanetary disk around TW Hya with the Atacama Large Millimeter/submillimeter Array. The ¹²CO/¹³CO ratio was estimated to be 21 ± 5 at disk radii of 70–110 au, which is significantly smaller than the value observed in the local interstellar medium, ∼69. It implies that an isotope exchange reaction occurs in a low-temperature environment with C/O > 1. In contrast, it is suggested that ¹²CO/¹³CO is higher than ∼84 in the outer disk (r > 130 au), which can be explained by the difference in the binding energy of the isotopologues on dust grains and the CO gas depletion processes. Our results imply that the gas-phase ¹²CO/¹³CO can vary by a factor of >4 even inside a protoplanetary disk and therefore can be used to trace material evolution in disks.

The transport of energetic charged particles (e.g., cosmic rays) in turbulent magnetic fields is usually characterized in terms of the diffusion parallel and perpendicular to a large-scale (or mean) magnetic field. The nonlinear guiding center theory has been a prominent perpendicular diffusion theory. A recent version of this theory, based on the random ballistic spreading of magnetic field lines and a backtracking correction (RBD/BC), has shown good agreement with test particle simulations for a two-component magnetic turbulence model. The aim of the present study is to test the generality of the improved theory by applying it to the noisy reduced magnetohydrodynamic (NRMHD) turbulence model, determining perpendicular diffusion coefficients that are compared with those from the field line random walk (FLRW) and unified nonlinear (UNLT) theories and our test particle simulations. The synthetic NRMHD turbulence model creates special conditions for energetic particle transport, with no magnetic fluctuations at higher parallel wavenumbers so there is no resonant parallel scattering if the particle Larmor radius R_L is even slightly smaller than the minimum resonant scale. This leads to nonmonotonic variation in the parallel mean free path λ_∥ with R_L. Among the theories considered, only RBD/BC matches simulations within a factor of 2 over the range of parameters considered. This accuracy is obtained even though the theory depends on λ_∥ and has no explicit dependence on R_L. In addition, the UNLT theory often provides accurate results, and even the FLRW limit provides a very simple and reasonable approximation in many cases.

We use a recent census of the Milky Way (MW) satellite galaxy population to constrain the lifetime of particle dark matter (DM). We consider two-body decaying dark matter (DDM) in which a heavy DM particle decays with lifetime τ comparable to the age of the universe to a lighter DM particle (with mass splitting ) and to a dark radiation species. These decays impart a characteristic “kick velocity,” V_kick = c, on the DM daughter particles, significantly depleting the DM content of low-mass subhalos and making them more susceptible to tidal disruption. We fit the suppression of the present-day DDM subhalo mass function (SHMF) as a function of τ and V_kick using a suite of high-resolution zoom-in simulations of MW-mass halos, and we validate this model on new DDM simulations of systems specifically chosen to resemble the MW. We implement our DDM SHMF predictions in a forward model that incorporates inhomogeneities in the spatial distribution and detectability of MW satellites and uncertainties in the mapping between galaxies and DM halos, the properties of the MW system, and the disruption of subhalos by the MW disk using an empirical model for the galaxy–halo connection. By comparing to the observed MW satellite population, we conservatively exclude DDM models with τ < 18 Gyr (29 Gyr) for V_kick = 20 kms⁻¹ (40 kms⁻¹) at 95% confidence. These constraints are among the most stringent and robust small-scale structure limits on the DM particle lifetime and strongly disfavor DDM models that have been proposed to alleviate the Hubble and S₈ tensions.

We report on a long-lasting, elevated gamma-ray flux state from VER J0521+211 observed by VERITAS, MAGIC, and Fermi-LAT in 2013 and 2014. The peak integral flux above 200 GeV measured with the nightly binned light curve is (8.8 ± 0.4) × 10⁻⁷ photons m⁻² s⁻¹, or ∼37% of the Crab Nebula flux. Multiwavelength observations from X-ray, UV, and optical instruments are also presented. A moderate correlation between the X-ray and TeV gamma-ray fluxes was observed, and the X-ray spectrum appeared harder when the flux was higher. Using the gamma-ray spectrum and four models of the extragalactic background light (EBL), a conservative 95% confidence upper limit on the redshift of the source was found to be z ≤ 0.31. Unlike the gamma-ray and X-ray bands, the optical flux did not increase significantly during the studied period compared to the archival low-state flux. The spectral variability from optical to X-ray bands suggests that the synchrotron peak of the spectral energy distribution (SED) may become broader during flaring states, which can be adequately described with a one-zone synchrotron self-Compton model varying the high-energy end of the underlying particle spectrum. The synchrotron peak frequency of the SED and the radio morphology of the jet from the MOJAVE program are consistent with the source being an intermediate-frequency-peaked BL Lac object.

The Multi-Order Solar Extreme Ultraviolet Spectrograph (MOSES) sounding rocket was launched from White Sands Missile Range on 2006 February 8th, to capture images of the Sun in the He ii 303.8 Å emission line. MOSES is a slitless spectrograph that forms images in multiple spectral orders simultaneously using a concave diffraction grating in an effort to measure line profiles over a wide field of view from a single exposure. Early work on MOSES data showed evidence of solar features composed of neither He ii 303.8 Å nor the nearby Si xi 303.3 Å spectral lines. We have built a forward model that uses cotemporal EIT images and the Chianti atomic database to fit synthetic images with known spectra to the MOSES data in order to quantify this additional spectral content. Our fit reveals a host of dim lines that alone are insignificant but combined contribute a comparable intensity to MOSES images as Si xi 303.3 Å. In total, lines other than He ii 303.8 Å and Si xi 303.3 Å contribute approximately 10% of the total intensity in the MOSES zero order image. This additional content, if not properly accounted for, could significantly impact the analysis of MOSES and similar slitless spectrograph data, especially those using a zero-order (undispersed) image. More broadly, this serves as a reminder that multilayer EUV imagers are sensitive to a host of weak contaminant lines.

We consider the effective field theory formulation of torsional gravity in a cosmological framework to alter the background evolution. Then we use the latest H₀ measurement from the SH0ES Team, as well as observational Hubble data from cosmic chronometer and radial baryon acoustic oscillations, and we reconstruct the f(T) form in a model-independent way by applying Gaussian processes. Since the special square-root term does not affect the evolution at the background level, we finally summarize a family of functions that can produce the background evolution required by the data. Lastly, performing a fitting using polynomial functions and implementing the Bayesian information criterion, we find an analytic expression that may describe the cosmological evolution in great agreement with observations.

In this work we conduct a thorough investigation of the X-ray and ultraviolet (UV) properties of Y Gem based on six archival XMM-Newton and Chandra observations to explore the nature of the system. The results show that Y Gem has strong (10^32–34 erg s⁻¹) X-ray emission, including a hard (with a maximum emission temperature of 8–16 keV) and a soft (with emission temperatures of 0.02–0.2 and 0.2–0.9 keV) component. The integrated UV luminosity of Y Gem reaches ∼10³⁵ erg s⁻¹. We show that the previous asymptotic giant branch-main-sequence (AGB-MS) Roche-lobe overflow (RLOF) scenario is dynamically unstable and can hardly explain the ∼10 keV X-ray emission temperature. We propose Y Gem as a symbiotic star, where a white dwarf (WD) accretes from its AGB companion based on its X-ray and UV properties. We make numerical simulations to examine the evolutionary history of this system. The simulations can produce the observed properties of Y Gem in the wind WRLOF scenario. An ∼0.8M_⊙ WD with a ∼1.0–1.8M_⊙ companion in a ∼2000–32,000 day initial orbit may evolve to a Y Gem-like system. Our finding implies a potential population of symbiotic stars that may have been misclassified as AGB-MS binaries. What is more, their high mass accretion rates may enable mass accumulation to the WD and makes them candidates of Type Ia supernovae progenitors.

Isolated neutron stars that are asymmetric with respect to their spin axis are possible sources of detectable continuous gravitational waves. This paper presents a fully coherent search for such signals from eighteen pulsars in data from LIGO and Virgo’s third observing run (O3). For known pulsars, efficient and sensitive matched-filter searches can be carried out if one assumes the gravitational radiation is phase-locked to the electromagnetic emission. In the search presented here, we relax this assumption and allow both the frequency and the time derivative of the frequency of the gravitational waves to vary in a small range around those inferred from electromagnetic observations. We find no evidence for continuous gravitational waves, and set upper limits on the strain amplitude for each target. These limits are more constraining for seven of the targets than the spin-down limit defined by ascribing all rotational energy loss to gravitational radiation. In an additional search, we look in O3 data for long-duration (hours–months) transient gravitational waves in the aftermath of pulsar glitches for six targets with a total of nine glitches. We report two marginal outliers from this search, but find no clear evidence for such emission either. The resulting duration-dependent strain upper limits do not surpass indirect energy constraints for any of these targets.

Relativistic spacecraft, like those proposed by the NASA Starlight program and the Breakthrough Starshot Initiative, will have to survive radiation production that is unique when compared to that experienced by conventional spacecraft. In a relativistic interstellar spacecraft’s reference frame, the interstellar medium (ISM) will look like a nearly monoenergetic beam of charged particles which impinges upon the leading edge of the spacecraft. Upon impact, ISM protons and electrons will travel characteristic lengths through the spacecraft shield and come to a stop via electronic and nuclear stopping mechanisms. As a result, bremsstrahlung photons will be produced within the spacecraft shield. In this work, we discuss the interstellar environment and its implications for radiation damage on relativistic spacecraft. We also explore expected radiation doses in terms of onboard device radiation tolerance.

Global coronal models seek to produce an accurate physical representation of the Sun’s atmosphere that can be used, for example, to drive space-weather models. Assessing their accuracy is a complex task, and there are multiple observational pathways to provide constraints and tune model parameters. Here, we combine several such independent constraints, defining a model-agnostic framework for standardized comparison. We require models to predict the distribution of coronal holes at the photosphere, and neutral line topology at the model’s outer boundary. We compare these predictions to extreme-ultraviolet (EUV) observations of coronal hole locations, white-light Carrington maps of the streamer belt, and the magnetic sector structure measured in situ by Parker Solar Probe and 1 au spacecraft. We study these metrics for potential field source surface (PFSS) models as a function of source surface height and magnetogram choice, as well as comparing to the more physical Wang–Sheeley–Arge (WSA) and the Magnetohydrodynamic Algorithm outside a Sphere (MAS) models. We find that simultaneous optimization of PFSS models to all three metrics is not currently possible, implying a trade-off between the quality of representation of coronal holes and streamer belt topology. WSA and MAS results show the additional physics that they include address this by flattening the streamer belt while maintaining coronal hole sizes, with MAS also improving coronal hole representation relative to WSA. We conclude that this framework is highly useful for inter- and intra-model comparisons. Integral to the framework is the standardization of observables required of each model, evaluating different model aspects.