Showing 1–50 of 1,577 results for author: Zhang, J

Asteroseismology and Dynamics Reveal Interior Structure and Coeval Evolution in the Triply Post-Main-Sequence system DG Leo

Authors: Ping Li, Wen-Ping Liao, Sheng-Bang Qian, Li-Ying Zhu, Jia Zhang, Qi-Bin Sun, Fang-Bin Meng

Abstract: $δ$ Scuti stars in binary or multiple systems serve as crucial probes for studying stellar pulsation and evolution. However, many such systems are not ideal for asteroseismology due to uncertainties in mass transfer with close companions and the challenges of dynamically measuring all components' physical properties. The triple system DG~Leo, comprising an inner binary and a distant $δ… ▽ More $δ$ Scuti stars in binary or multiple systems serve as crucial probes for studying stellar pulsation and evolution. However, many such systems are not ideal for asteroseismology due to uncertainties in mass transfer with close companions and the challenges of dynamically measuring all components' physical properties. The triple system DG~Leo, comprising an inner binary and a distant $δ$ Scuti star, is an ideal target due to its well-separated pulsator. By combining new \textit{TESS} photometry with archival spectroscopy, our dynamical analysis shows that the system's three components share similar masses, radii, and luminosities within errors, occupying coincident Hertzsprung--Russell diagram positions, indicative of coeval evolution. By fitting seven observed $δ$ Scuti frequencies through asteroseismic modeling with dynamically constrained theoretical grids, we simultaneously trace the pulsating star's evolution and constrain the triple system's evolutionary stage, with the derived fundamental parameters showing consistency with the dynamical solutions. Our analysis reveals that all three components of DG~Leo are in the post-main-sequence phase, with a system age of $0.7664^{+0.1402}_{-0.1258}$~Gyr. Additionally, the $δ$ Scuti component shows multiple non-radial modes with significant mixed-character frequencies, providing precise constraints on its convective core extent ($R_{\mathrm{cz}}/R = 0.0562^{+0.0137}_{-0.0021}$). △ Less

Submitted 24 December, 2025; originally announced December 2025.

Comments: In the pubilished version on ApJ, the operator S^2_2 means that S^2_m

Identifying Quasi-Periodic Micropulses in Pulsars with FAST Using Convolutional Neural Networks

Authors: Shidong Wang, Hui Liu, Ru-Shuang Zhao, Baoqiang Lao, Yong-Kun Zhang, Y. F. Xiao, Pei Wang, Di Li, R. W. Tian, Z. F. Tu, Q. Zhou, Z. J. Zhang, Qijun Zhi, Shijun Dang, Kun Yang

Abstract: Quasi-periodic MicroPulses (QMP) are quasi-periodic microstructural features manifested in individual pulsar radio pulses, the study of which is crucial for understanding pulsar radiation mechanisms. Manual identification of QMP in large-scale pulsar single-pulse datasets remains highly inefficient. To address this, we propose a Dual-Stage Residual Network (DSR) that achieves automated QMP detecti… ▽ More Quasi-periodic MicroPulses (QMP) are quasi-periodic microstructural features manifested in individual pulsar radio pulses, the study of which is crucial for understanding pulsar radiation mechanisms. Manual identification of QMP in large-scale pulsar single-pulse datasets remains highly inefficient. To address this, we propose a Dual-Stage Residual Network (DSR) that achieves automated QMP detection in FAST observational data through joint analysis of single-pulse profiles and their Amplitude Distribution Profiles (ADP), defined as the power spectra of the autocorrelation function derivatives of the microstructure residuals. The model was trained on PSR B1933+16 data from 2019 (10,486 single pulses) and evaluated on manually annotated PSR B1933+16 data from 2020 (9,657 single pulses). DSR achieved 96.10\% recall and 95.85\% precision on the test set. This approach provides an automated pipeline for large-scale, reproducible QMP identification and establishes the foundation for in-depth investigation of their physical mechanisms. △ Less

Submitted 22 December, 2025; originally announced December 2025.

Discussion on the vanishment of solar atmospheric structures during magnetic reconnection

Authors: Jun Zhang, Tao Ding, Yulei Wang

Abstract: In solar atmosphere, magnetic reconnection alters the topological connectivity, and magnetic energy is released. However, the length change of the reconnecting structures has rarely been reported. To identify the evolution of the topological structures, we search for reconnection events which should satisfy 3 criteria. (1) Each event displays an explicit X-type configuration, and the configuration… ▽ More In solar atmosphere, magnetic reconnection alters the topological connectivity, and magnetic energy is released. However, the length change of the reconnecting structures has rarely been reported. To identify the evolution of the topological structures, we search for reconnection events which should satisfy 3 criteria. (1) Each event displays an explicit X-type configuration, and the configuration consists of two sets of independent atmospheric structures, (2) the reconnection process is clearly observed, and (3) the topological connectivity of the structures can be tracked from at least 5 minutes prior to the occurrence of magnetic reconnection to 5 minutes after the reconnection. In this work, 3 events are selected and studied. During the reconnection moment, the total length of the two topological structures in each event shortens suddenly, and the decrements for events 1--3 are 47 Mm, 3.7 Mm, and 8.2 Mm, respectively, implying that partial structures vanish observationally during magnetic reconnection process. Several possibilities about the vanishment, e.g. the shrinkage of the reconnecting structures due to magnetic tension, the bizarre change in the third dimension, and magnetic field annihilation, have been discussed. △ Less

Submitted 17 December, 2025; originally announced December 2025.

Comments: 9 pages, 4 figures, 3 attached movies and 43 references

VLBI astrometry of radio stars to link radio and optical celestial reference frames III: 11 radio stars

Authors: Jingdong Zhang, Bo Zhang, Shuangjing Xu, Xiaofeng Mai, Mark J. Reid, Pengfei Jiang, Wen Chen, Fengchun Shu, Jinling Li, Lang Cui, Xingwu Zheng, Yan Sun, Zhaoxiang Qi

Abstract: The alignment between the radio-based International Celestial Reference Frame (ICRF) and the optical Gaia Celestial Reference Frame (Gaia-CRF) is critical for multi-waveband astronomy, yet systematic offsets at the optical bright end (G<13) limit their consistency. While radio stars offer a potential link between these frames, their utility has been restricted by the scarcity of precise Very Long… ▽ More The alignment between the radio-based International Celestial Reference Frame (ICRF) and the optical Gaia Celestial Reference Frame (Gaia-CRF) is critical for multi-waveband astronomy, yet systematic offsets at the optical bright end (G<13) limit their consistency. While radio stars offer a potential link between these frames, their utility has been restricted by the scarcity of precise Very Long Baseline Interferometry (VLBI) astrometry. In this study, we present new VLBI astrometry of 11 radio stars using the Very Long Baseline Array (VLBA), expanding the existing sample with positions, parallaxes, and proper motions measured. All 11 radio stars were detected, for 10 of which parallaxes and proper motions can be estimated, reaching a precision level of <1% in the best cases. These new samples greatly contribute to the link between ICRF and Gaia-CRF at the optical bright end. △ Less

Submitted 15 December, 2025; originally announced December 2025.

Comments: Submitted to MNRAS

Probing Periodic and Aperiodic Variability of X-ray Sources in M31, M81 and Centaurus A with Chandra

Authors: Jiachang Zhang, Zhiyuan Li, Ziqian Hua, Tong Bao

Abstract: Based on archival Chandra observations, we present a systematic timing survey of several hundred X-ray sources in M31, M81, and Centaurus A, mostly low-mass X-ray binaries (LXMBs), focusing on searching and characterizing aperiodic and periodic variability within single observation. We identify flares in 24 sources in M31, 5 in M81, and 26 in Cen~A; several display recurrent events. Flare duration… ▽ More Based on archival Chandra observations, we present a systematic timing survey of several hundred X-ray sources in M31, M81, and Centaurus A, mostly low-mass X-ray binaries (LXMBs), focusing on searching and characterizing aperiodic and periodic variability within single observation. We identify flares in 24 sources in M31, 5 in M81, and 26 in Cen~A; several display recurrent events. Flare durations span from tens of seconds to a few $10^{4}$ s, with peak luminosities of $10^{37}$-$10^{40}\ \mathrm{erg\ s^{-1}}$ and low flare duty cycles of $4.9\times10^{-6}$-$3.5\times10^{-2}$. Dipping events are found in 8 sources in M31, 1 in M81, and 5 in Cen A, including two repeaters. On multi-epoch baselines, the standard deviation of the source luminosity correlates linearly with the mean luminosity, with a coefficient of 0.49 (M31), 0.30 (M81), and 0.67 (Cen A), indicating galaxy-to-galaxy diversity. No statistically significant periodic signals are detected in M81 or Cen A, which, along with several periodic signals previously found among the M31 sources, can be understood considering a joint effect of our detection sensitivity and intrinsic distributions of the orbital period and X-ray luminosity of LMXBs. The ensemble of short-duty-cycle flares, a mix of recurrent and isolated dips, and galaxy-dependent rms--flux factor, supports a picture in which stochastic accretion-rate fluctuations modulate luminosity on $\sim$10-$10^{4}$ s. Conducted at known distances and across distinct host environments, this extragalactic survey provides uniform flare/dip samples and rms-flux scalings for bulge-dominated fields, offering empirical constraints for accretion physics and illustrating the promise of timing analyses in external galaxies using the Chandra archive. △ Less

Submitted 14 December, 2025; originally announced December 2025.

Comments: 17 pages, 7 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

Measurement of the cosmic ray nickel energy spectrum from 10 GeV/n to 2 TeV/n with the DAMPE

Authors: F. Alemanno, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, H. V. Boutin, I. Cagnoli, M. S. Cai, E. Casilli, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, Z. X. Chen, P. Coppin, M. Y. Cui, T. S. Cui, I. De Mitri, F. de Palma, A. Di Giovanni, T. K. Dong, Z. X. Dong, G. Donvito, J. L. Duan , et al. (123 additional authors not shown)

Abstract: Nickel, one of the most stable elements alongside iron, is the most abundant heavy element beyond iron in cosmic rays. With DAMPE's excellent charge resolution and broad energy range, a high-precision energy spectrum provides valuable insights into the acceleration sources of heavy nuclei and their propagation through the interstellar medium. In this analysis, we report the direct measurement of c… ▽ More Nickel, one of the most stable elements alongside iron, is the most abundant heavy element beyond iron in cosmic rays. With DAMPE's excellent charge resolution and broad energy range, a high-precision energy spectrum provides valuable insights into the acceleration sources of heavy nuclei and their propagation through the interstellar medium. In this analysis, we report the direct measurement of cosmic-ray nickel spectrum from 10 GeV/n to 2 TeV/n with nine years of flight data. The nickel spectrum is consistent with a single power law with spectral index -2.60 +/- 0.03 from 40 GeV/n to 1 TeV/n. This work provides an accurate measurement of differential flux of nickel with kinetic energy extending to TeV/n for the first time. △ Less

Submitted 12 December, 2025; originally announced December 2025.

Efficient pulsar distance measurement with multiple nanohertz gravitational-wave sources

Authors: Si-Ren Xiao, Ji-Yu Song, Yue Shao, Ling-Feng Wang, Jing-Fei Zhang, Xin Zhang

Abstract: In recent years, pulsar timing arrays (PTAs) have reported evidence for a nanohertz gravitational-wave (GW) background. As radio telescope sensitivity improves, PTAs are also expected to detect continuous gravitational waves from individual supermassive black hole binaries. Nanohertz GWs generate both Earth and pulsar terms in the timing data, and the time delay between the two terms encodes the p… ▽ More In recent years, pulsar timing arrays (PTAs) have reported evidence for a nanohertz gravitational-wave (GW) background. As radio telescope sensitivity improves, PTAs are also expected to detect continuous gravitational waves from individual supermassive black hole binaries. Nanohertz GWs generate both Earth and pulsar terms in the timing data, and the time delay between the two terms encodes the pulsar distance. Precise pulsar distance measurements are critical to fully exploiting pulsar-term information, which can improve the measurement precision of GW sources' sky position parameters and thus enhance the GW sky-localization capability. In this work, we propose a new pulsar distance estimation method by using pulsar-term phase information from GWs. We construct two-dimensional distance posteriors for pulsar pairs based on the simulated GW signals and combine them to constrain individual pulsar distances. Compared with the existing one-dimensional method, our approach reduces the impact of source-parameter uncertainties on pulsar distance measurements. Considering four GW sources and a PTA of 20 pulsars with a white-noise level of 20 ns, we find that a significant fraction of pulsars at distances $\lesssim 1.4$ kpc can achieve sub-parsec distance precision over a 15-year observation. △ Less

Submitted 11 December, 2025; originally announced December 2025.

Comments: 13 pages, 4 figures

X-ray Polarization and Spectral Variations in an Extreme High-Synchrotron-Peaked Blazar 1ES 1101--232

Authors: Xin-Ke Hu, Jin Zhang, Fei Xie, Xiang-Gao Wang

Abstract: We present the first X-ray polarimetric observation of the extreme high-synchrotron-peaked blazar 1ES 1101--232, conducted by the Imaging X-ray Polarimetry Explorer (IXPE). The data analysis incorporates simultaneous and quasi-simultaneous observations from Swift-XRT and NuSTAR. Our results reveal a significant detection of X-ray polarization in the 2--6 keV band at a confidence level (CL) of 6.6… ▽ More We present the first X-ray polarimetric observation of the extreme high-synchrotron-peaked blazar 1ES 1101--232, conducted by the Imaging X-ray Polarimetry Explorer (IXPE). The data analysis incorporates simultaneous and quasi-simultaneous observations from Swift-XRT and NuSTAR. Our results reveal a significant detection of X-ray polarization in the 2--6 keV band at a confidence level (CL) of 6.6$σ$, with a polarization degree of $Π_{\rm X}=17.9\%\pm2.7\%$ and an electric vector position angle (EVPA) of $ψ_{\rm X}=10^\circ.0\pm4^\circ.4$. An even higher polarization degree of $Π_{\rm X}=38.9\%\pm9.1\%$ with an EVPA of $ψ_{\rm X}=13^\circ.9\pm6^\circ.7$ is observed within a narrower time interval, at a CL of 4.3$σ$. During the IXPE observational campaign, the X-ray spectrum of 1ES 1101--232 exhibits a clear soft-to-hard spectral evolution in the 0.3--10 keV band, although no significant flux variability is detected. Additionally, a clockwise hysteresis loop is identified in the flux--photon index plane. These findings collectively indicate that the X-ray emission from 1ES 1101--232 originates in a region characterized by a well-ordered magnetic field through synchrotron radiation. △ Less

Submitted 10 December, 2025; originally announced December 2025.

Comments: 16 pages, 10 figures, 3 tables, accepted for publication in ApJ

Four Giant Planets from 2024 KMTNet Microlensing Campaign

Authors: Cheongho Han, Andrzej Udalski, Ian A. Bond, Chung-Uk Lee, Jiyuan Zhang, Michael D. Albrow, Sun-Ju Chung, Andrew Gould, Youn Kil Jung, Kyu-Ha Hwang, Yoon-Hyun Ryu, Yossi Shvartzvald, In-Gu Shin, Jennifer C. Yee, Weicheng Zang, Hongjing Yang, Doeon Kim, Dong-Jin Kim, Byeong-Gon Park, Przemek Mróz, Michał K. Szymański, Jan Skowron, Radosław Poleski, Igor Soszyński, Paweł Pietrukowicz , et al. (34 additional authors not shown)

Abstract: In this work, we present analyses of four newly discovered planetary microlensing events from the 2024 KMTNet survey season: KMT-2024-BLG-0176, KMT-2024-BLG-0349, KMT-2024-BLG-1870, and KMT-2024-BLG-2087. In each case, the planetary nature was revealed through distinct types of anomalies in the lensing light curves: a positive bump near the peak for KMT-2024-BLG-0176, an asymmetric peak for KMT-20… ▽ More In this work, we present analyses of four newly discovered planetary microlensing events from the 2024 KMTNet survey season: KMT-2024-BLG-0176, KMT-2024-BLG-0349, KMT-2024-BLG-1870, and KMT-2024-BLG-2087. In each case, the planetary nature was revealed through distinct types of anomalies in the lensing light curves: a positive bump near the peak for KMT-2024-BLG-0176, an asymmetric peak for KMT-2024-BLG-0349, a short-duration central dip for KMT-2024-BLG-1870, and a caustic-crossing feature for KMT-2024-BLG-2087. Detailed modeling of the light curves confirms that these anomalies are produced by planetary companions with planet-to-host mass ratios in the range of $(1.5\text{--}17.9)\times 10^{-3}$. Despite the diversity of signal morphologies, all planets detected in these events are giant planets with masses comparable to or exceeding that of Jupiter in the Solar System. Each planet orbits a host star less massive than the Sun, emphasizing the strength of microlensing in uncovering planetary systems around low-mass stellar hosts. △ Less

Submitted 10 December, 2025; originally announced December 2025.

Comments: 13 pages, 7 tables, 7 figures

A Test of Substellar Evolutionary Models with High-Precision Ages from Asteroseismology and Gyrochronology for the Benchmark System HR 7672AB

Authors: Yaguang Li, Michael C. Liu, Trent J. Dupuy, Daniel Huber, Jingwen Zhang, Daniel Hey, R. R. Costa, Jens Reersted Larsen, J. M. Joel Ong, Sarbani Basu, Travis S. Metcalfe, Yixiao Zhou, Jennifer van Saders, Timothy R. Bedding, Marc Hon, Hans Kjeldsen, Tiago L. Campante, Mário J. P. F. G. Monteiro, Mia Sloth Lundkvist, Mark Lykke Winther, Ashley Chontos, Nicholas Saunders, Theron W. Carmichael, Antonin Bouchez, Carlos Alvarez , et al. (13 additional authors not shown)

Abstract: We present high-precision measurements for HR 7672AB, composed of a Sun-like (G0V) star and an L dwarf companion. Three nights of precise (70 cm/s) radial velocity (RV) asteroseismology with the Keck Planet Finder clearly detect 5-minute oscillations from the primary HR 7672A, and modeling of the frequency spectrum yields an asteroseismic age of $1.87\pm0.65$ Gyr. We also determine a gyrochronolog… ▽ More We present high-precision measurements for HR 7672AB, composed of a Sun-like (G0V) star and an L dwarf companion. Three nights of precise (70 cm/s) radial velocity (RV) asteroseismology with the Keck Planet Finder clearly detect 5-minute oscillations from the primary HR 7672A, and modeling of the frequency spectrum yields an asteroseismic age of $1.87\pm0.65$ Gyr. We also determine a gyrochronological age of $2.58\pm0.47$ Gyr, and we combine these two results for a final age of $2.26\pm0.40$ Gyr. In addition, we obtained new RVs for HR 7672A and new astrometry for the companion HR 7672B. From a joint orbit fit, we measured a dynamical mass of $1.111\pm0.017$ $M_\odot$ for HR 7672A and $75.39\pm0.67$ $M_{\rm Jup}$ for HR 7672B. This places the companion near the stellar/substellar boundary and thus particularly sensitive to differences in model predictions. The joint precision in host star age (18\% uncertainty) and companion mass (0.9\% uncertainty) makes HR 7672AB an exceptional substellar benchmark. Combined with the companion's luminosity, we use these measurements to test predictions from six brown dwarf cooling models. The best agreement occurs with the Chabrier et al. (2023) models, which incorporate a new equation of state, resulting in predictions that agree within $<$0.3$σ$ with all the observations. The other 5 sets of models agree at the 1--3$σ$ level depending on the particular test, and some models struggle to predict a sufficient low luminosity for HR 7672B at any age given its dynamical mass. Finally, we detected a weak seismic signal in near-simultaneous TESS photometry of HR 7672A, with the resulting RV-to-photometry oscillation amplitude ratio consistent with solar values. △ Less

Submitted 5 December, 2025; originally announced December 2025.

Comments: 30 pages, 15 figures, submitted to ApJ, comments welcome

A Persistently Active Fast Radio Burst source Embedded in an Expanding Supernova Remnant

Authors: Chen-Hui Niu, Di Li, Yuan-Pei Yang, Yuhao Zhu, Yongkun Zhang, Jia-heng Zhang, Zexin Du, Jumei Yao, Xiaoping Zheng, Pei Wang, Yi Feng, Bing Zhang, Weiwei Zhu, Wenfei Yu, Ji-an Jiang, Shi Dai, Chao-Wei Tsai, A. M. Chen, Yijun Hou, Jiarui Niu, Weiyang Wang, Chenchen Miao, Xinming Li, Junshuo Zhang

Abstract: Fast radio bursts (FRBs) remain one of the most puzzling astrophysical phenomena. While most FRBs are detected only once or sporadically, we present the identification of FRB 20190520B as the first persistently active source over a continuous span of ~ four years. This rare long-term activity enabled a detailed investigation of its dispersion measure (DM) evolution. We also report that FRB 2019052… ▽ More Fast radio bursts (FRBs) remain one of the most puzzling astrophysical phenomena. While most FRBs are detected only once or sporadically, we present the identification of FRB 20190520B as the first persistently active source over a continuous span of ~ four years. This rare long-term activity enabled a detailed investigation of its dispersion measure (DM) evolution. We also report that FRB 20190520B exhibits a substantial decrease in DM at a global rate of minus 12.4 plus or minus 0.3 pc cm^-3 yr^-1, exceeding previous FRB DM variation measurements by a factor of three and surpassing those observed in pulsars by orders of magnitude. The magnitude and consistency of the DM evolution, along with a high host DM contribution, strongly indicate that the source resides in a dense, expanding ionized medium, likely a young supernova remnant (SNR). △ Less

Submitted 5 December, 2025; originally announced December 2025.

Mini-supernovae from white dwarf-neutron star mergers: Viewing-angle-dependent spectra and lightcurves

Authors: Yacheng Kang, Jin-Ping Zhu, Lijing Shao, Jiahang Zhong, Jinghao Zhang, Bing Zhang

Abstract: Unstable mass transfer may occur during white dwarf-neutron star (WD-NS) mergers, in which the WD can be tidally disrupted and form an accretion disk around the NS. Such an accretion disk can produce unbound wind ejecta, with synthesized $^{56}\mathrm{Ni}$ mixed in. Numerical simulations reveal that this unbound ejecta should be strongly polar-dominated, which may cause the following radioactive-p… ▽ More Unstable mass transfer may occur during white dwarf-neutron star (WD-NS) mergers, in which the WD can be tidally disrupted and form an accretion disk around the NS. Such an accretion disk can produce unbound wind ejecta, with synthesized $^{56}\mathrm{Ni}$ mixed in. Numerical simulations reveal that this unbound ejecta should be strongly polar-dominated, which may cause the following radioactive-powered thermal transient to be viewing-angle-dependent. This issue has so far received limited investigation. We investigate how the intrinsically non-spherical geometry of WD-NS wind ejecta affects the viewing-angle dependence of the thermal transients. Using a two-dimensional axisymmetric ejecta configuration and incorporating heating from the radioactive decay of $^{56}\mathrm{Ni}$, we employ a semi-analytical discretization scheme to simulate the observed viewing-angle-dependent photospheric evolution, as well as the resulting spectra and lightcurves. The observed photosphere evolves over time and depends strongly on the viewing angle: off-axis observers can see deeper, hotter inner layers of the ejecta and larger projected photospheric areas compared to on-axis observers. For a fiducial WD-NS merger producing 0.3 solar mass of ejecta and 0.01 solar mass of synthesized $^{56}\mathrm{Ni}$, the resulting peak optical absolute magnitudes of the transient span from ~ -12 mag along the polar direction to ~ -16 mag along the equatorial direction, corresponding to luminosities of $10^{40}$-$10^{42}$ erg s$^{-1}$. The typical peak timescales are expected to be 3-10 d. We for the first time explore the viewing-angle effect on WD-NS merger transients. Since their ejecta composition and energy sources resemble those of supernovae, yet WD-NS merger transients are dimmer and evolve more rapidly, we propose using "mini-supernovae" to describe the thermal emission following WD-NS mergers. △ Less

Submitted 3 December, 2025; originally announced December 2025.

Comments: Under final review at A&A after minor revisions, 14 pages, 7 figures

Statistical and Temporal Analysis of Multi-component Burst-clusters from the Repeating FRB 20190520B

Authors: Jia-heng Zhang, Chen-Hui Niu, Yu-hao Zhu, Di Li, Yu Wang, Wei-yang Wang, Yi Feng, Xin-ming Li, Jia-rui Niu, Pei Wang, Yun-wei Yu, Yong-kun Zhang, Xiao-ping Zheng

Abstract: Fast Radio Bursts (FRBs) are bright, millisecond-duration extragalactic radio transients that probe extreme astrophysical environments. Many FRBs exhibit multi-component structures, which encode information about their emission mechanisms or progenitor systems and thus provide important clues to their origins. In this work, we systematically analyze the burst morphology of FRB 20190520B and compar… ▽ More Fast Radio Bursts (FRBs) are bright, millisecond-duration extragalactic radio transients that probe extreme astrophysical environments. Many FRBs exhibit multi-component structures, which encode information about their emission mechanisms or progenitor systems and thus provide important clues to their origins. In this work, we systematically analyze the burst morphology of FRB 20190520B and compare component distributions across four active FRBs observed with FAST: FRB 20121102A, FRB 20190520B, FRB 20201124A, and FRB 20240114A. We find that multi-component burst-clusters show spectral properties similar to single-peak bursts, and no periodicity is detected in their temporal behavior. The component-count distributions follow a power law, revealing scale-free behavior consistent with self-organized criticality (SOC) processes. Multi-component clusters account for 12-30% of all detected bursts, regardless of source activity, providing new insights into burst-to-burst variability and the physical processes driving FRB emission. △ Less

Submitted 3 December, 2025; v1 submitted 3 December, 2025; originally announced December 2025.

The first extragalactic ultra-compact X-ray binary : a candidate black hole-white dwarf system

Authors: Qian-Qi Ma, Jiachang Zhang, Wei-Min Gu, Zhiyuan Li, Shan-Shan Weng, Tong Bao

Abstract: M31 UCXB-1 is one of the brightest X-ray point sources in the bulge of M31, with a peak X-ray luminosity $ L_{\mathrm{0.5-10 \: keV}} = 2.9^{+0.2}_{-0.2} \times 10^{38} \: \mathrm{erg} \: \mathrm{s}^{-1} $. Both XMM-Newton and Chandra observations have detected an eclipsing signal with a period of about 465 seconds from this source, and we note that the periodic signal is detected exclusively duri… ▽ More M31 UCXB-1 is one of the brightest X-ray point sources in the bulge of M31, with a peak X-ray luminosity $ L_{\mathrm{0.5-10 \: keV}} = 2.9^{+0.2}_{-0.2} \times 10^{38} \: \mathrm{erg} \: \mathrm{s}^{-1} $. Both XMM-Newton and Chandra observations have detected an eclipsing signal with a period of about 465 seconds from this source, and we note that the periodic signal is detected exclusively during the source's high-luminosity states. This signal probably originates from its orbital motion, therefore it is an ultra-compact X-ray binary (UCXB) candidate with the highest X-ray luminosity. Our theoretical analyses show that M31 UCXB-1 is in good agreement with the luminosity-orbital period relation ($ L_{\mathrm{2-10 \: keV}}-P_{\mathrm{orb}} $) of the black hole/neutron star--white dwarf (BH/NS--WD) UCXB system. Moreover, our spectral analyses indicate that the primary in M31 UCXB-1 is more likely to be a BH rather than an NS. The results show that M31 UCXB-1 is a BH--WD system, with the shortest orbital period, the possibly strongest gravitational wave emission, and the most massive white dwarf among the known UCXBs. △ Less

Submitted 1 December, 2025; originally announced December 2025.

Comments: 18 pages, 8 figures, author's version, accepted for publication in The Innovation

Images of shadow and thin accretion disk around Bardeen black hole surrounded by perfect fluid dark matter

Authors: Haiyuan Feng, Ziqiang Cai, Hao-Peng Yan, Rong-Jia Yang, Jinjun Zhang

Abstract: We investigated the shadow and optical appearance of Bardeen black hole (BH) immersed in perfect-fluid dark matter (PFDM). Using the EHT data, we find that the DM parameter is restricted to a narrow allowed range, confined to values of $\mathcal{O}(10^{-1}-10^{-2})$. Additionally, we observed that increasing the DM parameter substantially enlarges the photon sphere, the critical impact parameter,… ▽ More We investigated the shadow and optical appearance of Bardeen black hole (BH) immersed in perfect-fluid dark matter (PFDM). Using the EHT data, we find that the DM parameter is restricted to a narrow allowed range, confined to values of $\mathcal{O}(10^{-1}-10^{-2})$. Additionally, we observed that increasing the DM parameter substantially enlarges the photon sphere, the critical impact parameter, and thus the shadow radius, whereas the magnetic charge $g$ produces only negligible corrections. The DM component also modifies the optical appearance of the accretion disk: higher $b$ systematically suppresses the observed radiation intensity and reduces image brightness, while changes in $g$ yield only marginal effects. Subsequently, using the Novikov-Thorne thin disk model, we analyze primary and secondary images, observed flux, and redshift patterns, showing that PFDM noticeably alters image size and brightness whereas magnetic charge has a negligible influence. No blueshifted regions appear in any configuration. These results highlight several promising observational signatures for testing DM environments and nonlinear electrodynamic effects around BHs. △ Less

Submitted 30 November, 2025; originally announced December 2025.

Comments: 44 pages, 86 figures

Sulfur monoxide as a tracer of the Galactic $^{32}$S/$^{34}$S gradient

Authors: Yipeng Zou, Jiangshui Zhang, Dingyuan Wei, Yaoting Yan, Donatella Romano, Youxin Wang, Jialiang Chen, Hongzhi Yu, Jieyu Zhao

Abstract: To date, the Galactic interstellar radial $^{32}$S/$^{34}$S gradient has only been studied with the CS isotopologs, which may be affected by uncertainties due to the use of a single tracer. As another abundant S-bearing molecules, SO and its isotopomer $^{34}$SO could be considered as tracers of the $^{32}$S/$^{34}$S ratio. We present the first systematic observations of SO and $^{34}$SO toward a… ▽ More To date, the Galactic interstellar radial $^{32}$S/$^{34}$S gradient has only been studied with the CS isotopologs, which may be affected by uncertainties due to the use of a single tracer. As another abundant S-bearing molecules, SO and its isotopomer $^{34}$SO could be considered as tracers of the $^{32}$S/$^{34}$S ratio. We present the first systematic observations of SO and $^{34}$SO toward a large sample of molecular clouds with accurate distances, performed with the IRAM 30 m and the 10 m Submillimeter Telescope (SMT). With the IRAM 30 m, SO $2_2-1_1$ was detected in 59 of 82 sources ($\sim$82%), and $^{34}$SO $2_2-1_1$ in 8 sources ($\sim$10%). With the SMT 10 m, SO $5_5-4_4$ was detected in 136 of 184 sources ($\sim$74%), and $^{34}$SO $5_5-4_4$ in 55 of 77 strong SO sources ($\sim$72%). SO/$^{34}$SO ratios were derived for 8 ($2_2-1_1$) and 55 ($5_5-4_4$) sources. No correlation was found between the SO/$^{34}$SO ratio and heliocentric distance or $T_k$, suggesting negligible distance and fractionation effects. Both LTE and non-LTE analyses consistently suggest that the optical depth effect is also insignificant. $^{32}$S/$^{34}$S ratios from the $2_2-1_1$ transitions follow the increasing radial trend proposed by previous CS species measurements, while those from the $5_5-4_4$ lines are systematically lower. The lower transitions of SO and $^{34}$SO may be suitable tracers of $^{32}$S/$^{34}$S, though the detections are rare. Comparisons between measurements and Galactic chemical evolution model suggest that the nucleosynthesis prescriptions need to be revised in the low-metallicity regime, but more data for the outermost Galactic regions are crucial for drawing strong conclusions. △ Less

Submitted 28 November, 2025; originally announced November 2025.

Comments: 25 pages, 12 figures, 3 tables + Appendices. Accepted for publication in The Astrophysical Journal Supplement Series

Robust evidence for dynamical dark energy in light of DESI DR2 and joint ACT, SPT, and Planck data

Authors: Tian-Nuo Li, Guo-Hong Du, Sheng-Han Zhou, Yun-He Li, Jing-Fei Zhang, Xin Zhang

Abstract: Recent baryon acoustic oscillation (BAO) measurements released by DESI, when combined with cosmic microwave background (CMB) data and type Ia supernova (SN) data, suggest a significant preference for dynamical dark energy (DDE) that exhibits the phantom-like behavior in the past and has transitioned into quintessence-like behavior today. In this work, we conduct a comprehensive analysis of six rep… ▽ More Recent baryon acoustic oscillation (BAO) measurements released by DESI, when combined with cosmic microwave background (CMB) data and type Ia supernova (SN) data, suggest a significant preference for dynamical dark energy (DDE) that exhibits the phantom-like behavior in the past and has transitioned into quintessence-like behavior today. In this work, we conduct a comprehensive analysis of six representative DDE parametrization models by utilizing the latest and most precise CMB data jointly from ACT, SPT, and Planck, in conjunction with BAO data from DESI DR2 and SN data from DESY5, PantheonPlus, and Union3. Our overall analysis indicates that the preference for DDE in the Quintom-B regime remains robust, regardless of the DDE parameterization model and the data combination employed. The trend of this preference is significantly strengthened with the support of DESY5 SN data. Specifically, when using the CMB+DESI+DESY5 data, for the Barboza-Alcaniz (BA) model, we obtain $w_0 = -0.785 \pm 0.047$ and $w_a = -0.43^{+0.10}_{-0.09}$, which significantly deviate from the $Λ$CDM values and provide evidence for DDE at the $4.2σ$ level. By the reconstruction of the dark energy equation of state $w(z)$, normalized dark energy density $f_{\mathrm{DE}}(z)$, and the deceleration parameter $q(z)$, we also observe clear departures from $Λ$CDM, further reinforcing the case for DDE. Furthermore, the Bayesian evidence analysis indicates that the Chevallier-Polarski-Linder, BA and Exponential models are moderately favored relative to $Λ$CDM based on the CMB+DESI+DESY5 data. △ Less

Submitted 27 November, 2025; originally announced November 2025.

Comments: 13 pages, 4 figures

A Catalogue of Mid-infrared Variable Sources from unTimely

Authors: Zihan kang, Jingyi Zhang, Yanxia Zhang, Changhua Li, Xiao Kong, Minzhi Kong, Jinghang Shi, Shirui Wei, Xue-Bing Wu

Abstract: The WISE and NEOWISE missions have provided the only mid-infrared all-sky time-domain data, opening a unique observational window for variability studies. Yet, a comprehensive and systematic catalog of mid-infrared variable sources has remained unavailable. In this work, we construct the first large-scale mid-infrared variability catalog based on the unTimely coadded photometry, covering tens of m… ▽ More The WISE and NEOWISE missions have provided the only mid-infrared all-sky time-domain data, opening a unique observational window for variability studies. Yet, a comprehensive and systematic catalog of mid-infrared variable sources has remained unavailable. In this work, we construct the first large-scale mid-infrared variability catalog based on the unTimely coadded photometry, covering tens of millions of sources. By employing a Bayesian Gaussian mixture model with a Dirichlet process, we identified 8,256,042 variable sources in the W1 band and 7,147,661 in the W2 band, significantly expanding the landscape of known mid-infrared variables. In addition to robust variability metrics, our analysis highlights rare and extreme outliers through dedicated outlier-detection algorithms, enabling the discovery of unusual classes of objects such as eruptive young stellar objects, highly variable active galactic nuclei, and other rare transients. This unprecedented dataset provides a new foundation for time-domain astronomy in the mid-infrared, offering complementary insights to optical and near-infrared surveys, and opening the door to systematic investigations of stellar evolution, accretion processes, and dust-enshrouded astrophysical environments on a Galactic and extragalactic scale. △ Less

Submitted 26 November, 2025; originally announced November 2025.

Radio Burst Phenomenology of AD Leonis and Associated Signatures of Propagation Effects

Authors: Jiale Zhang, Harish K. Vedantham, Joseph R. Callingham, Hui Tian

Abstract: We present the high-resolution radio dynamic spectra of AD Leonis (AD Leo) between 1.0 and 1.5 GHz taken by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) on Dec. 1st, 2023. Over a 15-minute period, we identify complex, superimposed spectro-temporal structures, including: (1) broadband, second-long modulation lanes with downward frequency drifts, (2) narrowband ($\approx$ 50 MHz)… ▽ More We present the high-resolution radio dynamic spectra of AD Leonis (AD Leo) between 1.0 and 1.5 GHz taken by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) on Dec. 1st, 2023. Over a 15-minute period, we identify complex, superimposed spectro-temporal structures, including: (1) broadband, second-long modulation lanes with downward frequency drifts, (2) narrowband ($\approx$ 50 MHz), short-duration S-burst envelopes with upward drifts, and (3) even narrower ($\approx$ 10 MHz), millisecond-scale S-burst striae within these envelopes. Using the discrete Fourier transform and auto-correlation function, we identify two dominant periodic emission patterns, corresponding to the periodicities of the S-bursts ($\approx0.1$ s) and the striae ($\approx0.01$ s). The complex superposition of diverse time-frequency structures poses a challenge to interpreting all the emission variability as intrinsic to the source. We propose that the modulation lanes could be a propagation effect as the radio waves traverse an inhomogeneous, regularly structured plasma region in the AD Leo's magnetosphere. By modelling a plasma screen with sinusoidal phase variation in one dimension, we show that we could qualitatively reconstruct the observed modulation lanes. The origin of the finest structures, the striae, remains unclear. Our work highlights that propagation effects in the stellar magnetosphere can potentially probe kilometre-scale structures in the emission regions and provide novel constraints on density inhomogeneities caused by magnetohydrodynamic waves that are difficult to access by other means. △ Less

Submitted 25 November, 2025; originally announced November 2025.

Comments: Accepted for publication in ApJ

SE3D: Building a radiative transfer emulator to fit panchromatic resolved galaxy observations with 3D models of dust and stars

Authors: Steven Ramnichal, Junkai Zhang, Stijn Wuyts, Cheng Li

Abstract: We present a framework for analysing panchromatic and spatially resolved galaxy observations, dubbed SE3D. SE3D simultaneously and self-consistently models a galaxy's spectral energy distribution and its spectral distributions of global structural parameters: the wavelength-dependent galaxy size, light profile and projected axis ratio. To this end, it employs a machine learning emulator trained on… ▽ More We present a framework for analysing panchromatic and spatially resolved galaxy observations, dubbed SE3D. SE3D simultaneously and self-consistently models a galaxy's spectral energy distribution and its spectral distributions of global structural parameters: the wavelength-dependent galaxy size, light profile and projected axis ratio. To this end, it employs a machine learning emulator trained on a large library of toy model galaxies processed with 3D dust radiative transfer and mock-observed under a range of viewing angles. The toy models vary in their stellar and dust geometries, and include radial stellar population gradients. The computationally efficient machine learning emulator uses a Bayesian neural network architecture, and reproduces the spectral distributions at an accuracy of ~ 0.05 dex or less across the dynamic range of input parameters, and across the rest-frame UVJ colour space spanned by observed galaxies. We carry out a sensitivity analysis demonstrating that the emulator has successfully learned the intricate mappings between galaxy physical properties and direct observables (fluxes, colours, sizes, size ratios between different wavebands, ...). We further discuss the physical conditions giving rise to a range of total-to-selective attenuation ratios, Rv, with among them most prominently the projected dust surface mass density. △ Less

Submitted 24 November, 2025; originally announced November 2025.

Comments: Submitted to MNRAS. 18 pages, 14 figures, 2 tables

SE3D: Testing the recovery of stellar population, dust and structural properties on mock-observed toy model and simulated galaxies

Authors: Junkai Zhang, Steven Ramnichal, Stijn Wuyts, Cheng Li

Abstract: The translation from direct observables to physical properties of galaxies is a key step in reconstructing their evolutionary histories. Variations in stellar populations and star-dust geometry can induce inhomogeneous mass-to-light ratios, complicating this process. SE3D is a novel modelling framework, built around a radiative transfer emulator, aimed at tackling this problem. In this paper, we t… ▽ More The translation from direct observables to physical properties of galaxies is a key step in reconstructing their evolutionary histories. Variations in stellar populations and star-dust geometry can induce inhomogeneous mass-to-light ratios, complicating this process. SE3D is a novel modelling framework, built around a radiative transfer emulator, aimed at tackling this problem. In this paper, we test the ability of SE3D to recover known intrinsic properties of toy model and TNG50 simulated galaxies from mock observations of their multi-wavelength photometric and structural properties. We find an encouraging performance for several key characteristics, including the bulk stellar mass, dust mass and SFR, as well as their respective radial extents. We point out limitations, and investigate the impact of various sources of model mismatch. Among them, mismatch in the shapes of star formation histories contributes most, with radial and azimuthal structure and stellar metallicity distributions playing a progressively more minor role. We also analyse the evolution from z=2 to z=0 of resolved stellar and dust properties of TNG galaxies, as measured intrinsically and expressed in their distribution across UVJ and IRX-$β$ diagnostic diagrams. We test different methods to assign dust to the simulation, and find a persistent lack of Mdust/Mstar evolution and a more limited dynamic range across the diagnostic diagrams compared to observations. △ Less

Submitted 24 November, 2025; originally announced November 2025.

Comments: Submitted to MNRAS. 20 pages, 11 figures, 3 tables

Aql X-1 from dawn 'til dusk: the early rise, fast state transition and decay of its 2024 outburst

Authors: A. Marino, F. Coti Zelati, K. Alabarta, D. M. Russell, Y. Cavecchi, N. Rea, S. K. Rout, T. Di Salvo, J. Homan, Á. Jurado-López, L. Ji, R. Soria, T. D. Russell, Y. L. Wang, A. Anitra, M. C. Baglio, H. Feng, S. Fijma, S. Guillot, Y. F. Huang, G. Illiano, M. Imbrogno, C. Jin, F. Lewis, Y. F. Liang , et al. (14 additional authors not shown)

Abstract: Transient Low-Mass X-ray Binaries (LMXBs) are usually first detected by all-sky X-ray monitors when they enter new outbursts, typically at X-ray luminosities above $\sim$10$^{36}$ erg/s. Observations of these sources during the early rise of the outbursts have so far been very limited. However, the launch of the Einstein Probe (EP) has greatly improved our ability to detect fainter X-ray activity,… ▽ More Transient Low-Mass X-ray Binaries (LMXBs) are usually first detected by all-sky X-ray monitors when they enter new outbursts, typically at X-ray luminosities above $\sim$10$^{36}$ erg/s. Observations of these sources during the early rise of the outbursts have so far been very limited. However, the launch of the Einstein Probe (EP) has greatly improved our ability to detect fainter X-ray activity, unlocking access to the outburst early rise. In September 2024, EP detected the early onset of a new outburst from the neutron star LMXB Aql X-1, catching the source at a luminosity below 10$^{35}$ erg/s. In this paper we present results from a comprehensive, multi-wavelength campaign of this event, combining data from EP, NICER, NuSTAR, Swift and Las Cumbres Observatory covering the full outburst from its early rise through its decay. By comparing X-ray and optical light curves obtained with Las Cumbres Observatory during the initial rise, we show that the start of the X-ray emission lagged the optical rise by, at most, 3 days. Time-resolved X-ray spectroscopy revealed how the geometry and the physical properties of the accretion flow evolve during this early stage of the outburst, as well as at higher luminosities as the source transitioned through the canonical X-ray spectral states - hard, intermediate and soft. These data show that the source underwent a very rapid, about 12-h long, transition from the hard to the soft state about two weeks after the optical onset of the outburst. The evolution of the temperature and physical sizes of both the inner region of the disk and a black body near the NS surface suggest that at the state transition, a boundary and spreading layer likely formed. We discuss these results in the context of time-scales for outburst evolution and state transitions in accreting neutron stars and black holes. △ Less

Submitted 20 November, 2025; originally announced November 2025.

Comments: 13 pages, 9 figures, submitted to A&A

Detectability of axion-like dark matter for different time-delay interferometry combinations in space-based gravitational wave detectors

Authors: Yong-Yong Liu, Jing-Rui Zhang, Ming-Hui Du, He-Shan Liu, Peng Xu, Yun-Long Zhang

Abstract: In the space-based gravitational wave detections, the axion-like dark matter would alter the polarization state of the laser link between spacecrafts due to the birefringence effect. However, current designs of space-based laser interferometer are insensitive to variations in the polarization angle. Thus, the additional wave plates are employed to enable the response of the axion-induced birefring… ▽ More In the space-based gravitational wave detections, the axion-like dark matter would alter the polarization state of the laser link between spacecrafts due to the birefringence effect. However, current designs of space-based laser interferometer are insensitive to variations in the polarization angle. Thus, the additional wave plates are employed to enable the response of the axion-induced birefringence effect. We calculate and compare the sensitivities of different space-based detectors, accounting for three time-delay interferometry combinations, including Monitor, Beacon, and Relay. We find that the Monitor and Beacon combinations have better sensitivity in the high-frequency range, and the optimal sensitivity reaches $g_{aγ}\sim 10^{-13}\text{GeV}^{-1}$, while the Sagnac combination is superior in the low-frequency range. We also find that ASTROD-GW can cover the detection range of axion-like dark matter mass down to $10^{-20}\text{eV}$. △ Less

Submitted 19 November, 2025; originally announced November 2025.

Comments: 9 pages, 12 figures

Variable-temperature attenuator calibration method for on-wafer microwave noise characterization of low-noise amplifiers

Authors: Anthony J. Ardizzi, Jiayin Zhang, Akim A. Babenko, Kieran A. Cleary, Austin J. Minnich

Abstract: Low-noise cryogenic microwave amplifiers are widely used in applications such as radio astronomy and quantum computing. On-wafer noise characterization of cryogenic low-noise transistors is desirable because it facilitates more rapid characterization of devices prior to packaging, but obtaining accurate noise measurements is difficult due to the uncertainty arising from the input loss and temperat… ▽ More Low-noise cryogenic microwave amplifiers are widely used in applications such as radio astronomy and quantum computing. On-wafer noise characterization of cryogenic low-noise transistors is desirable because it facilitates more rapid characterization of devices prior to packaging, but obtaining accurate noise measurements is difficult due to the uncertainty arising from the input loss and temperature gradients prior to the device-under-test (DUT). Here, we report a calibration method that enables the simultaneous determination of the backend noise temperature and effective-noise-ratio at the input plane of the DUT. The method is based on measuring the S-parameters and noise power of a series of attenuators at two or more distinct physical temperatures. We validate our method by measuring the noise temperature of InP HEMTs in 4-8 GHz. The calibration method can be generalized to measure the microwave noise temperature of any two-port device so long as a series of attenuators can be measured at two or more distinct physical temperatures. △ Less

Submitted 17 November, 2025; originally announced November 2025.

Comments: 10 pages, 7 figures, 3 tables, 11 equations

Constraining the Neutral Hydrogen Fraction from SKA Simulated Observation using a Double-Gaussian Decomposition Technique

Authors: Jiajun Zhang, Huanyuan Shan

Abstract: The Epoch of Reionization (EoR) is a unique phase in cosmic history, marked by the ionization of neutral hydrogen by the first luminous sources. The global neutral hydrogen fraction (x_HI) is a key observable for probing this era. This paper presents a novel, statistically robust method to extract the evolution of x_HI from the challenging noise-dominated data from the Square Kilometre Array (SKA)… ▽ More The Epoch of Reionization (EoR) is a unique phase in cosmic history, marked by the ionization of neutral hydrogen by the first luminous sources. The global neutral hydrogen fraction (x_HI) is a key observable for probing this era. This paper presents a novel, statistically robust method to extract the evolution of x_HI from the challenging noise-dominated data from the Square Kilometre Array (SKA) Data Challenge 3b. Our approach is based on a key physical insight: the pixel value distribution in SKA intensity maps is a mixture of signals from ionized and neutral regions. We model this distribution as a superposition of two Gaussian components-one fixed at zero representing noise and ionized bubbles, and a second, offset Gaussian tracing the neutral hydrogen signal. We perform this decomposition on data grouped into three redshift bins. The double-Gaussian model provides an excellent fit to the pixel histogram data. The derived x_HI values show a clear decreasing trend across the three redshift bins, consistent with a progressing reionization process. And the results are consistent with the provided simulation data. This method offers a powerful, model-independent, and fully interpretable way for measuring x_HI from 21 cm data, demonstrating significant potential for application to future SKA observations. △ Less

Submitted 17 November, 2025; originally announced November 2025.

Wide-Field X-ray Polarimetry for High Energy Astronomical Transients: First results of the pathfinder CXPD Cubesat Mission

Authors: Hong-Bang Liu, Zu-Ke Feng, Huan-Bo Feng, Di-Fan Yi, Li-Rong Xie, Yan-Jun Xie, Zong-Wang Fan, Jin Zhang, Wen-Jin Xie, Xue-Feng Huang, Wei Deng, Fei Xie, Dong Wang, Zi-Li Li, Hui Wang, Ran Chen, Shi-Qiang Zhou, Kai Chen, Jin Li, Qian Liu, Shi Chen, Rui-Ting Ma, Bin-Long Wang, Zhen-Yu Tang, Hang-Zhou Li , et al. (5 additional authors not shown)

Abstract: The Low Energy Polarization Detector (LPD) is a key component of the next-generation large-scale Gamma-Ray Burst polarimeter, POLAR-2. It is designed for polarization observations of transient sources in the soft X-ray energy range with a wide field of view (FOV). To validate the key technologies required for wide-FOV X-ray polarization measurements, the Cosmic X-ray Polarization Detector (CXPD) C… ▽ More The Low Energy Polarization Detector (LPD) is a key component of the next-generation large-scale Gamma-Ray Burst polarimeter, POLAR-2. It is designed for polarization observations of transient sources in the soft X-ray energy range with a wide field of view (FOV). To validate the key technologies required for wide-FOV X-ray polarization measurements, the Cosmic X-ray Polarization Detector (CXPD) CubeSat was developed as a prototype for the LPD. The CXPD is equipped with two Gas Microchannel Plate Pixel Detectors (GMPDs) that measure X-ray polarization via the photoelectric effect, where ejected photoelectrons produce ionization tracks in the gas which are imaged to reconstruct their emission directions. Laboratory calibrations of the modulation factor and energy spectra were successfully performed using linear polarized X-ray sources at 2.98 keV, 4.51 keV, 6.40 keV, and 8.05 keV. Since its launch in June 2023, the CXPD has successfully completed critical in-orbit technology verification. It has also performed polarization observations of two bright X-ray sources Sco X-1 and the transient Swift J1727.8-1613 yielding constraints on their polarization degrees and angles. Notably, this was the first time that an anti-coincidence detector had been implemented in an X-ray polarimeter, enabling in-orbit verification of the charged-particle background rejection algorithm. These results demonstrate the feasibility of wide-field soft X-ray polarization measurements and provide essential guidance for the development of the LPD for the POLAR-2 mission, thereby advancing the frontier of X-ray polarization astronomy. △ Less

Submitted 17 November, 2025; originally announced November 2025.

Gravitational wave standard sirens from GWTC-3 combined with DESI DR2 and DESY5: A late-universe probe of the Hubble constant and dark energy

Authors: Ji-Yu Song, Guo-Hong Du, Tian-Nuo Li, Ling-Feng Wang, Jing-Zhao Qi, Jing-Fei Zhang, Xin Zhang

Abstract: Recently, the combination of the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2) baryon acoustic oscillation (BAO) data and the Planck cosmic microwave background (CMB) measurements has shown a $\sim$3$σ$ preference for a dynamical dark energy model with a phantom-crossing behavior. However, such a phantom-crossing dark energy evolution further exacerbates the already severe Hubbl… ▽ More Recently, the combination of the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2) baryon acoustic oscillation (BAO) data and the Planck cosmic microwave background (CMB) measurements has shown a $\sim$3$σ$ preference for a dynamical dark energy model with a phantom-crossing behavior. However, such a phantom-crossing dark energy evolution further exacerbates the already severe Hubble tension in the $Λ$CDM model. Moreover, there exists a $\sim2σ$ tension between the DESI DR2 BAO and CMB datasets. Therefore, it is essential to measure the Hubble constant and dark-energy equation-of-state (EoS) parameters using only late-universe observations. In this work, we investigate a novel late-universe data combination: gravitational-wave (GW) standard sirens, BAO, and Type Ia supernovae (SNe Ia). This combination provides a fully distance-ladder- and CMB-independent determination of the Hubble constant and the dark-energy EoS. Using 47 GW standard sirens from the third Gravitational-Wave Transient Catalog, the DESI DR2 BAO data, and DESY5 SNe Ia data, in the $w_0w_a$CDM model, we obtain $H_0=74.8^{+6.3}_{-8.9}$ km s$^{-1}$ Mpc$^{-1}$, $Ω_{\rm m}=0.320^{+0.015}_{-0.012}$, $w_0=-0.775^{+0.072}_{-0.074}$, and $w_a=-0.80\pm0.47$, indicating a mild phantom-crossing behavior within the $1σ$ credible interval with an $H_0$ value consistent with the distance ladder measurements. Our analysis demonstrates the power of GW standard sirens in breaking parameter degeneracies, and this novel data combination provides joint constraints on the Hubble constant and the dark-energy EoS parameters. △ Less

Submitted 14 November, 2025; originally announced November 2025.

Comments: 10 pages, 3 figures

Galaxy clusters from the DESI Legacy Imaging Surveys -- III. Star-forming fraction of brightest cluster galaxies

Authors: Shufei Liu, Hu Zou, Jinfu Gou, Weijian Guo, Niu Li, Wenxiong Li, Gaurav Singh, Haoming Song, Jipeng Sui, Xi Tan, Yunao Xiao, Jingyi Zhang, Lu Feng

Abstract: This study investigates the evolution of the star-forming fraction ($F_{\mathrm{sf}}$) of Brightest Cluster Galaxies (BCGs) at $z<0.8$, using the galaxy clusters identified from the Legacy Imaging Surveys from the Dark Energy Spectroscopic Instrument (DESI). Star-forming galaxies are identified using the $g-z$ color, and $F_{\mathrm{sf}}$ is measured as a function of redshift, cluster halo mass, a… ▽ More This study investigates the evolution of the star-forming fraction ($F_{\mathrm{sf}}$) of Brightest Cluster Galaxies (BCGs) at $z<0.8$, using the galaxy clusters identified from the Legacy Imaging Surveys from the Dark Energy Spectroscopic Instrument (DESI). Star-forming galaxies are identified using the $g-z$ color, and $F_{\mathrm{sf}}$ is measured as a function of redshift, cluster halo mass, and galaxy stellar mass. Field galaxies are used as a comparison sample to reduce selection effects. For BCGs, $F_{\mathrm{sf}}$ increases with redshift, showing a slow rise below $z \sim 0.4 - 0.5$ and a more rapid increase above this range. In contrast, $F_{\mathrm{sf}}$ decreases with increasing cluster halo mass and BCG stellar mass. At the low stellar mass end, BCGs exhibit higher star-forming fractions than field galaxies, suggesting enhanced star formation likely fueled by cold gas accretion from the intracluster medium. Also, star-forming BCGs tend to show larger projected offsets from the optical cluster density peak than quenching BCGs, indicating ongoing assembly. The analysis of the specific star formation rate (sSFR) further indicates a transition in the dominant mechanism driving star formation in BCGs: cooling flows are likely responsible at low redshift, while gas-rich mergers play a greater role at higher redshift. The shift in dominance occurs around $z \sim 0.5$, aligning with the steep rise in $F_{\mathrm{sf}}$ of BCG. △ Less

Submitted 2 December, 2025; v1 submitted 12 November, 2025; originally announced November 2025.

Journal ref: 2025MNRAS.544.3350L

CoronaGraph Instrument Reference stars for Exoplanets (CorGI-REx) I. Preliminary Vetting and Implications for the Roman Coronagraph and Habitable Worlds Observatory

Authors: Justin Hom, Schuyler G. Wolff, Catherine A. Clark, David R. Ciardi, Sarah J. Deveny, Steve B. Howell, Alexandra Z. Greenbaum, Colin Littlefield, Ramya M. Anche, Vanessa P. Bailey, Wolfgang Brandner, Gaël Chauvin, Julien H. Girard, Brian Kern, Eric Mamajek, Bertrand Mennesson, Dmitry Savransky, Karl R. Stapelfeldt, Beth A. Biller, Marah Brinjikji, Masayuki Kuzuhara, Maxwell A. Millar-Blanchaer, Toshiyuki Mizuki, Nicholas T. Schragal, Macarena C. Vega-Pallauta , et al. (6 additional authors not shown)

Abstract: The upcoming Roman Coronagraph will be the first high-contrast instrument in space capable of high-order wavefront sensing and control technologies, a critical technology demonstration for the proposed Habitable Worlds Observatory (HWO) that aims to directly image and characterize habitable exoEarths. The nominal Roman Coronagraph observing plan involves alternating observations of a science targe… ▽ More The upcoming Roman Coronagraph will be the first high-contrast instrument in space capable of high-order wavefront sensing and control technologies, a critical technology demonstration for the proposed Habitable Worlds Observatory (HWO) that aims to directly image and characterize habitable exoEarths. The nominal Roman Coronagraph observing plan involves alternating observations of a science target and a bright, nearby reference star. High contrast is achieved using wavefront sensing and control, also known as "digging a dark hole", where performance depends on the properties of the reference star, requiring V<3, a resolved stellar diameter <2 mas, and no stellar multiplicity. The imposed brightness and diameter criteria limit the sample of reference star candidates to high-mass main sequence and post-main sequence objects, where multiplicity rates are high. A future HWO coronagraph may have similarly restrictive criteria in reference star selection. From an exhaustive literature review of 95 stars, we identify an initial list of 40 primary and 18 reserve reference star candidates relevant to both the Roman Coronagraph and HWO. We present results from an initial survey of these candidates with high-resolution adaptive optics imaging and speckle interferometry and identify no new companions. We discuss the need for higher-contrast observations to sufficiently vet these reference star candidates prior to Roman Coronagraph observations along with the implications of reference star criteria on observation planning for Roman and HWO. △ Less

Submitted 11 November, 2025; originally announced November 2025.

Comments: Accepted for Publication in AJ, 27 pages, 8 figures, 6 tables

Journal ref: AJ 171 36 (2026)

Massive stars exploding in a He-rich circumstellar medium XII. SN 2024acyl: A fast, linearly declining Type Ibn supernova with early flash-ionisation features

Authors: Y. -Z. Cai, A. Pastorello, K. Maeda, J. -W. Zhao, Z. -Y. Wang, Z. -H. Peng, A. Reguitti, L. Tartaglia, A. V. Filippenko, Y. Pan, G. Valerin, B. Kumar, Z. Wang, M. Fraser, J. P. Anderson, S. Benetti, S. Bose, T. G. Brink, E. Cappellaro, T. -W. Chen, X. -L. Chen, N. Elias-Rosa, A. Esamdin, A. Gal-Yam, M. González-Bañuelos , et al. (41 additional authors not shown)

Abstract: We present a photometric and spectroscopic analysis of the Type Ibn supernova (SN) 2024acyl. It rises to an absolute magnitude peak of about -17.58 mag in 10.6 days, and displays a rapid linear post-peak light-curve decline in all bands, similar to most SNe Ibn. The optical pseudobolometric light curve peaks at ($3.5\pm0.8) \times 10^{42}$ erg s$^{-1}$, with a total radiated energy of… ▽ More We present a photometric and spectroscopic analysis of the Type Ibn supernova (SN) 2024acyl. It rises to an absolute magnitude peak of about -17.58 mag in 10.6 days, and displays a rapid linear post-peak light-curve decline in all bands, similar to most SNe Ibn. The optical pseudobolometric light curve peaks at ($3.5\pm0.8) \times 10^{42}$ erg s$^{-1}$, with a total radiated energy of $(5.0\pm0.4) \times 10^{48}$ erg. The spectra are dominated by a blue continuum at early stages, with narrow P-Cygni \Hei~lines and flash-ionisation emission lines of C {\sc iii}, N {\sc iii}, and He {\sc ii}. The P-Cygni \Hei~features gradually evolve and become emission-dominated in late-time spectra. The \Ha~line is detected throughout the entire spectral evolution, which indicates that the CSM is helium-rich with some residual amount of H. Our multiband light-curve modelling yields estimates of the ejecta mass of $M_{ej}$ = $0.98^{+0.30}_{-0.20} \, \msun$, with a kinetic energy of $E_{k} = 0.13^{+0.03}_{-0.02} \times 10^{51}$ erg, and a $^{56}Ni$ mass of $M_{\mathrm{Ni}} = 0.017 \, \msun$. The inferred CSM properties are characterised by a mass of $M_{\rm{CSM}} = 0.39^{+0.04}_{-0.04}$ \msun, an inner radius of $R_0$=$15.6^{+1.9}_{-2.0}$ AU, and a density $ρ_{CSM} = (1.32\pm0.22)\times10^{-11} \, \mathrm{g\,cm^{-3}}$. The multi-epoch spectra are well reproduced by the CMFGEN/ \texttt{he4p0} model, corresponding to a He-ZAMS mass of 4~M$_\odot$. These findings are consistent with a scenario of an SN powered by ejecta-CSM interaction, originating from a low-mass helium star that evolved within an interacting binary system where the CSM with some residual hydrogen may originate from the mass-transfer process. In addition, a channel of core-collapse explosion of a late-type Wolf-Rayet star with H, or an Ofpe/WN9 star with fallback accretion, cannot be entirely ruled out. △ Less

Submitted 6 November, 2025; originally announced November 2025.

Comments: 19 pages, 12 figures

Hadronic Processes in Advection-Dominated Accretion Flow as the Origin of TeV Excesses in BL Lac Objects

Authors: Ji-Shun Lian, Ze-Rui Wang, Jin Zhang

Abstract: The spectral energy distributions (SEDs) of certain BL Lac objects (BL Lacs) exhibit an additional hard $γ$-ray component in the TeV energy range that surpasses the predictions of the one-zone leptonic jet model. The origin of this excess emission remains unclear. In this study, we selected five BL Lacs whose SEDs display a very hard intrinsic spectrum in the TeV band and successfully reproduced t… ▽ More The spectral energy distributions (SEDs) of certain BL Lac objects (BL Lacs) exhibit an additional hard $γ$-ray component in the TeV energy range that surpasses the predictions of the one-zone leptonic jet model. The origin of this excess emission remains unclear. In this study, we selected five BL Lacs whose SEDs display a very hard intrinsic spectrum in the TeV band and successfully reproduced their broadband SEDs using a two-zone lepto-hadronic model. Within this framework, the emission observed in the optical, X-ray, GeV $γ$-ray, and sub-TeV $γ$-ray bands is modeled using the synchrotron and synchrotron self-Compton radiation processes of the relativistic electrons in the jets. Meanwhile, the TeV excess is attributed to $γ$-ray emission resulting from the photomeson ($pγ$) process via $π^0$ decay occurring within advection-dominated accretion flows (ADAFs). This scenario requires a hard proton spectrum with a spectral index of $p \sim 1.6-1.7$ and a cutoff energy ranging from 30 to 90 TeV, as well as a relatively large ADAF radius. Such hard proton spectra suggest that the dominant acceleration mechanisms are likely magnetic reconnection and/or stochastic acceleration processes within ADAFs. Additionally, the emission from the cascaded electrons results in a bump in the keV--MeV band; however, it is overwhelmed by the jet emission. Although the hadronuclear ($pp$) process cannot be entirely ruled out, it would necessitate an even harder proton spectrum and a higher cutoff energy compared to the $pγ$ process, making it a less favorable explanation for the observed TeV excess. △ Less

Submitted 8 November, 2025; v1 submitted 6 November, 2025; originally announced November 2025.

Comments: 13 pages, 2 Figures, 1 Table. Accepted for publication in ApJ

Machine-Learning Estimation of Energy Fractions in MHD Turbulence Modes

Authors: Jiyao Zhang, Yue Hu

Abstract: Magnetohydrodynamic (MHD) turbulence plays a central role in many astrophysical processes in the interstellar medium (ISM), including star formation, heat conduction, and cosmic-ray scattering. MHD turbulence can be decomposed into three fundamental modes-fast, slow, and Alfvén-each contributing differently to the dynamics of the medium. However, characterizing and separating the energy fractions… ▽ More Magnetohydrodynamic (MHD) turbulence plays a central role in many astrophysical processes in the interstellar medium (ISM), including star formation, heat conduction, and cosmic-ray scattering. MHD turbulence can be decomposed into three fundamental modes-fast, slow, and Alfvén-each contributing differently to the dynamics of the medium. However, characterizing and separating the energy fractions of these modes was challenging due to the limited information available from observations. To address this difficulty, we use 3D isothermal and multiphase MHD turbulence simulations to examine how mode energy fractions vary under different physical conditions. Overall, we find that the Alfvén and slow modes carry comparable kinetic-energy fractions and together dominate the turbulent energy budget in multiphase media, while the fast mode contributes the smallest fraction. Relative to isothermal conditions, multiphase simulations exhibit an enhanced fast-mode energy fraction. We further introduce a machine-learning-based approach that employs a conditional Residual Neural Network to infer these fractions directly from spectroscopic data. The method leverages the fact that the three MHD modes imprint distinct morphological signatures in spectroscopic maps owing to their differing anisotropies and compressibilities. Our model is trained on a suite of isothermal and multiphase simulations covering typical ISM conditions. We further demonstrate that our machine learning model can robustly recover the mode fractions from spectroscopic observables, achieving mean absolute errors of approximately 0.05 for seen data and 0.1 for unseen data. △ Less

Submitted 6 November, 2025; originally announced November 2025.

Comments: 10 pages, 6 figures, submitted to ApJ

Super amplification of lunar response to gravitational waves driven by thick crust

Authors: Lei Zhang, Jinhai Zhang, Han Yan, Xian Chen

Abstract: The Moon has been long regarded as a natural resonator of gravitational waves (GWs) since 1960, showing great potential to fill the frequency gap left behind GW detections by ground- or space-based laser interferometry. However, the spatial variation of this amplification capacity on the Moon remains unclear. Here, we numerically simulate the lunar response to GWs by fully considering the fluctuan… ▽ More The Moon has been long regarded as a natural resonator of gravitational waves (GWs) since 1960, showing great potential to fill the frequency gap left behind GW detections by ground- or space-based laser interferometry. However, the spatial variation of this amplification capacity on the Moon remains unclear. Here, we numerically simulate the lunar response to GWs by fully considering the fluctuant topography and laterally heterogeneous interior structures. Our results show that most regions on the Moon can amplify GWs with a ratio over 2, a finding significantly higher than previous estimations. Particularly, the amplification ratio can even reach factors of tens at the resonant frequency of ~0.015 Hz on the highlands surrounding the South Pole-Aitken (SPA) basin, where the regional crust is the thickest. Our findings establish the thick-crust regions as critical zones of GW amplification, which is essential for future landing site selection and instrumental setting for GW detection on the Moon. △ Less

Submitted 6 November, 2025; originally announced November 2025.

ASTROFLOW: A Real-Time End-to-End Pipeline for Radio Single-Pulse Searches

Authors: Guanhong Lin, Dejia Zhou, Jianli Zhang, Jialang Ding, Fei Liu, Xiaoyun Ma, Yuan Liang, Ruan Duan, Liaoyuan Liu, Xuanyu Wang, Xiaohui Yan, Yingrou Zhan, Yuting Chu, Jing Qiao, Wei Wang, Jie Zhang, Zerui Wang, Meng Liu, Chenchen Miao, Menquan Liu, Meng Guo, Di Li, Pei Wang

Abstract: Fast radio bursts (FRBs) are extremely bright, millisecond duration cosmic transients of unknown origin. The growing number of wide-field and high-time-resolution radio surveys, particularly with next-generation facilities such as the SKA and MeerKAT, will dramatically increase FRB discovery rates, but also produce data volumes that overwhelm conventional search pipelines. Real-time detection thus… ▽ More Fast radio bursts (FRBs) are extremely bright, millisecond duration cosmic transients of unknown origin. The growing number of wide-field and high-time-resolution radio surveys, particularly with next-generation facilities such as the SKA and MeerKAT, will dramatically increase FRB discovery rates, but also produce data volumes that overwhelm conventional search pipelines. Real-time detection thus demands software that is both algorithmically robust and computationally efficient. We present Astroflow, an end-to-end, GPU-accelerated pipeline for single-pulse detection in radio time-frequency data. Built on a unified C++/CUDA core with a Python interface, Astroflow integrates RFI excision, incoherent dedispersion, dynamic-spectrum tiling, and a YOLO-based deep detector. Through vectorized memory access, shared-memory tiling, and OpenMP parallelism, it achieves 10x faster-than-real-time processing on consumer GPUs for a typical 150 s, 2048-channel observation, while preserving high sensitivity across a wide range of pulse widths and dispersion measures. These results establish the feasibility of a fully integrated, GPU-accelerated single-pulse search stack, capable of scaling to the data volumes expected from upcoming large-scale surveys. Astroflow offers a reusable and deployable solution for real-time transient discovery, and provides a framework that can be continuously refined with new data and models. △ Less

Submitted 4 November, 2025; originally announced November 2025.

Comments: 17 pages, 14 figures

Conditional variational autoencoders for cosmological model discrimination and anomaly detection in cosmic microwave background power spectra

Authors: Tian-Yang Sun, Tian-Nuo Li, He Wang, Jing-Fei Zhang, Xin Zhang

Abstract: The cosmic microwave background power spectra are a primary window into the early universe. However, achieving interpretable, likelihood-compatible compression and fast inference under weak model assumptions remains challenging. We propose a parameter-conditioned variational autoencoder (CVAE) that aligns a data-driven latent representation with cosmological parameters while remaining compatible w… ▽ More The cosmic microwave background power spectra are a primary window into the early universe. However, achieving interpretable, likelihood-compatible compression and fast inference under weak model assumptions remains challenging. We propose a parameter-conditioned variational autoencoder (CVAE) that aligns a data-driven latent representation with cosmological parameters while remaining compatible with standard likelihood analyses. The model achieves high-fidelity compression of the $D_\ell^{TT}$, $D_\ell^{EE}$, and $D_\ell^{TE}$ spectra into just 5 latent dimensions, with reconstruction accuracy exceeding $99.9\%$ within Planck uncertainties. It reliably reconstructs spectra for beyond-$Λ$CDM scenarios, even under parameter extrapolation, and enables rapid inference, reducing the computation time from $\sim$40 hours to $\sim$2 minutes while maintaining posterior consistency. The learned latent space demonstrates a physically meaningful structure, capturing a distributed representation that mirrors known cosmological parameters and their degeneracies. Moreover, it supports highly effective unsupervised discrimination among cosmological models, achieving performance competitive with supervised approaches. Overall, this physics-informed CVAE enables anomaly detection beyond $Λ$CDM and points to physically meaningful directions for refinement. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Comments: 19 pages, 13 figures

An extremely fast fading population II dwarf nova candidate: caught spectroscopically on the rise

Authors: Natasha Van Bemmel, Jielai Zhang, Jeff Cooke, Anais Möller, Igor Andreoni, Katie Auchettl, David Buckley, Jonathan Carney, Dougal Dobie, James Freeburn, Bruce Gendre, Vanshika Kansal, Itumeleng Monageng, Arne Rau, Nikita Rawat, Mark Suhr, Edward N. Taylor

Abstract: We present AT2022kak, a rapidly evolving optical transient discovered by the KiloNova and Transients Program (KNTraP). This interesting burst exhibited extremely fast evolution, with a large amplitude blue outburst of m > 3.3 in a single night, and a rapid fade back to quiescence in the following two nights. We deployed a multi-wavelength follow-up campaign, monitoring the object for the next two… ▽ More We present AT2022kak, a rapidly evolving optical transient discovered by the KiloNova and Transients Program (KNTraP). This interesting burst exhibited extremely fast evolution, with a large amplitude blue outburst of m > 3.3 in a single night, and a rapid fade back to quiescence in the following two nights. We deployed a multi-wavelength follow-up campaign, monitoring the object for the next two months, but saw no recurrent burst. Three years later, while observing to get spectroscopy of the object in quiescence, there was a new outburst, enabling the collection of time-resolved spectra of the rise and fade of the outburst. The light curve properties of the first burst and spectra of the second burst are consistent with a dwarf nova. Its fast evolving behaviour makes it one of the fastest and faintest dwarf novae observed. The estimated distance of AT2022kak from the Galactic centre is ~6.6 kpc, with a scale height of ~2 kpc. This scale height places it in the Galactic thick disk, where only very few dwarf novae have been found, and is therefore a potential Population II dwarf novae system. △ Less

Submitted 18 November, 2025; v1 submitted 30 October, 2025; originally announced October 2025.

Comments: 10 pages, 9 figures, 3 tables, submitted to MNRAS

Mapping Anisotropies in the Stochastic Gravitational-Wave Background with space detector networks

Authors: Zhi-Yuan Li, Zheng-Cheng Liang, Cong-mao Zhang, Jian-dong Zhang, Yi-Ming Hu

Abstract: Future space-based gravitational-wave detectors such as TianQin, LISA, and Taiji are expected to conduct joint observations. Such a multi-detector network will provide complementary viewing angles for the anisotropic stochastic gravitational-wave background (SGWB), thereby significantly enhancing the capability to reconstruct and localize its spatial distribution. In this paper, we have establishe… ▽ More Future space-based gravitational-wave detectors such as TianQin, LISA, and Taiji are expected to conduct joint observations. Such a multi-detector network will provide complementary viewing angles for the anisotropic stochastic gravitational-wave background (SGWB), thereby significantly enhancing the capability to reconstruct and localize its spatial distribution. In this paper, we have established the first dedicated data analysis pipeline for the anisotropic stochastic gravitational-wave background using a joint network of TianQin, LISA, and Taiji. Our analysis incorporates both Gaussian, stationary, and unpolarized point sources from diverse sky locations as well as a random sky map. We have performed full-sky map reconstruction in pixel space using maximum likelihood estimation to extract the angular distribution of the SGWB. The results demonstrate that, when considering the detector noise, the TianQin+LISA+Taiji detector network can reconstruct the angular power spectrum of the stochastic background up to a maximum multipole moment of $l = 14 $, which can provide valuable information for studies on the spatial distribution of galactic compact binaries and physical imprints from the early Universe. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Model-independent late-universe measurements of $H_0$ and $Ω_\mathrm{K}$ with the PAge-improved inverse distance ladder

Authors: Guo-Hong Du, Tian-Nuo Li, Jia-Le Ling, Yan-Hong Yao, Jing-Fei Zhang, Xin Zhang

Abstract: The standard $Λ{\rm CDM}$ model has encountered serious challenges and the $H_0$ tension has become more significant with increasingly precise cosmological observation. Meanwhile, inconsistencies in measurements of the curvature parameter $Ω_\mathrm{K}$ between different datasets also have emerged. In this work, we employ two global and cosmic age-based parameterizations, PAge and MAPAge, to perfo… ▽ More The standard $Λ{\rm CDM}$ model has encountered serious challenges and the $H_0$ tension has become more significant with increasingly precise cosmological observation. Meanwhile, inconsistencies in measurements of the curvature parameter $Ω_\mathrm{K}$ between different datasets also have emerged. In this work, we employ two global and cosmic age-based parameterizations, PAge and MAPAge, to perform model-independent measurements of the Hubble constant $H_0$ and $Ω_\mathrm{K}$ by utilizing the inverse distance ladder (IDL). To construct the PAge-improved IDL, we utilize the strong gravitational lensing (SGL), cosmic chronometers (CC), and gamma ray bursts (GRB) data to calibrate the latest DESI DR2 baryon acoustic oscillation data and DESY5 type Ia supernova data. Our analysis indicate that DESI+DESY5+SGL+CC+GRB gives $H_0=71.59\pm 0.94\,{\rm km}~{\rm s}^{-1}~{\rm Mpc}^{-1}$ in the MAPAge model, reducing the $H_0$ tension to the $1.0σ$ level. Extending to MAPAge$+Ω_{\rm K}$ model, we obtain $Ω_\mathrm{K}=0.001\pm 0.038$, which suggests that current late-time data are consistent with a flat universe. Finally, the Bayesian analysis indicates that the present late-universe data provide weak to moderate evidence in favor of PAge and MAPAge relative to $Λ{\rm CDM}$. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Comments: 12 pages, 2 figures

Multi-Faceted Emission Properties of PSR J2129+4119 Observed with FAST

Authors: Habtamu Menberu Tedila, Di Li, Pei Wang, Rai Yuen, Ziwei Wu, Shijun Dang, Jianping Yuan, Na Wang, Marilyn Cruces, Jun Shuo Zhang, Juntao Bai, De Zhao, FAST Collaboration

Abstract: We present a detailed single-pulse study of the long-period pulsar PSR J2129+4119 using high-sensitivity FAST observations. Despite locating well below the traditional death line, the pulsar exhibits sustained and multi-modal emission behavior, including nulls, weak pulses, regular emission, and occasional bright pulses. The nulling fraction is measured to be $8.13\% \pm 0.51\%$, with null duratio… ▽ More We present a detailed single-pulse study of the long-period pulsar PSR J2129+4119 using high-sensitivity FAST observations. Despite locating well below the traditional death line, the pulsar exhibits sustained and multi-modal emission behavior, including nulls, weak pulses, regular emission, and occasional bright pulses. The nulling fraction is measured to be $8.13\% \pm 0.51\%$, with null durations typically under four pulse periods. Fluctuation spectral analysis reveals both phase-modulated subpulse drifting and intermittent beat-like modulation. At the same time, polarization profiles show high linear polarization and stable polarization position angle (PPA) swings consistent with a near-tangential sightline geometry. Quasi-periodic microstructures are detected in 11.54\% of regular pulses, with a mean periodicity and width of 4.57 ms and 4.30 ms, respectively. A well-defined scintillation arc in the secondary spectrum confirms the presence of a localized scattering screen. These results indicate that PSR J2129+4119 remains magnetospherically active and coherently emitting despite its low energy loss rate, offering key insights into pulsar emission physics near the death line. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Comments: 22 pages, 18 figures, Revised for ApJ

Evidence of cosmic-ray acceleration up to sub-PeV energies in the supernova remnant IC 443

Authors: Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, C. M. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, G. H. Chen, H. X. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen, S. H. Chen , et al. (291 additional authors not shown)

Abstract: Supernova remnants (SNRs) have been considered as the primary contributors to cosmic rays (CRs) in our Galaxy. However, the maximum energy of particles that can be accelerated by shocks of SNRs is uncertain observationally and theoretically, and the role of contribution to CRs around PeV energies by SNRs is unclear. In this study, we present observations of high-energy $γ$-ray emission from the SN… ▽ More Supernova remnants (SNRs) have been considered as the primary contributors to cosmic rays (CRs) in our Galaxy. However, the maximum energy of particles that can be accelerated by shocks of SNRs is uncertain observationally and theoretically, and the role of contribution to CRs around PeV energies by SNRs is unclear. In this study, we present observations of high-energy $γ$-ray emission from the SNR IC 443 using the Large High Altitude Air Shower Observatory (LHAASO). The morphological analysis reveals a pointlike source whose location and spectrum are consistent with those of the Fermi-LAT-detected compact source with $π^0$-decay signature, and a more extended source which is consistent with a newly discovered source, previously unrecognized by Fermi-LAT. The spectrum of the point source can be described by a power-law function with an index of $\sim3.0$, extending beyond $\sim 30$ TeV without apparent cutoff. Assuming a hadronic origin of the $γ$-ray emission, the $95\%$ lower limit of accelerated protons reaches about 300 TeV. The extended source might be coincident with IC 443, SNR G189.6+3.3 or the putative pulsar wind nebula CXOU J061705.3+222127, and can be explained by either a hadronic or leptonic model. The LHAASO results provide compelling evidence that CR protons up to sub-PeV energies can be accelerated by the SNR. △ Less

Submitted 29 October, 2025; originally announced October 2025.

Accretion rates of stellar-mass compact objects embedded in AGN discs

Authors: Cheng-Liang Jiao, Liying Zhu, Er-gang Zhao, Jia Zhang

Abstract: Stellar-mass compact objects (COs) embedded in active galactic nucleus (AGN) discs are commonly assumed to accrete via Bondi or Bondi-Hoyle-Lyttleton (BHL) prescriptions, neglecting gas angular momentum. We show that differential rotation in AGN discs can impart non-negligible angular momentum, in which case accretion proceeds through a viscous disc rather than Bondi/BHL flow. Our model provides a… ▽ More Stellar-mass compact objects (COs) embedded in active galactic nucleus (AGN) discs are commonly assumed to accrete via Bondi or Bondi-Hoyle-Lyttleton (BHL) prescriptions, neglecting gas angular momentum. We show that differential rotation in AGN discs can impart non-negligible angular momentum, in which case accretion proceeds through a viscous disc rather than Bondi/BHL flow. Our model provides a new framework estimating the CO accretion rate as $\dot{M}_\mathrm{CO} = \min\{\dot{M}_\mathrm{vis}, \dot{M}_\mathrm{BHL}\}$, where the viscous rate $\dot{M}_\mathrm{vis}$ accounts for gas--CO relative motion decomposed into a local gradient term (due to differential rotation) and bulk motion (from differing orbital parameters). This rate can be expressed as $\dot{M}_\mathrm{vis} = αξ(r_\mathrm{H}/r_\mathrm{BHL})^3\dot{M}_\mathrm{BHL}$, where $ξ$ is a coefficient of order unity. It can also be approximately scaled to the global AGN accretion rate as $\dot{M}_\mathrm{vis} \propto \dot{M}_1$, with the scaling coefficients in both forms determined by the specific dynamical configuration. The accretion is viscosity-limited when $q > [αξ(1+\mathcal{M}^2)^{3}/3]^{1/2} h^3$, where $q$ is the mass ratio between the CO and the supermassive black hole, $α$ the viscosity parameter, $\mathcal{M}$ the Mach number of the bulk relative motion, and $h$ the aspect ratio of the AGN disc. In thin AGN discs this condition is satisfied for most stellar-mass or more massive COs. Our framework also naturally allows for the inclusion of established outflow corrections, thereby enabling a more realistic treatment of super-Eddington flows. Our formulation thus improves upon Bondi/BHL prescriptions and offers a more physically motivated basis for studying CO evolution in AGN environments. △ Less

Submitted 29 October, 2025; originally announced October 2025.

Comments: 14 pages, 5 figures, accepted for publication in MNRAS

Journal ref: Mon Not R Astron Soc (2025) 2024-2037

Engulfment of Eccentric Planets by Giant Stars: Hydrodynamics and Light Curves

Authors: Mengqi Yang, Dong Lai, Fuyuan Wu, Jie Zhang

Abstract: Recent observations suggest that planetary engulfment by a giant star may produce radiation that resembles subluminous red novae. We present three-dimensional hydrodynamical simulations of the interaction between an eccentric $5 \,M_J$ giant planet and its $1\,M_\odot$ red-giant host star. The planet's pericenter is initially $60\%$ of the stellar radius and is fully engulfed after tens of orbits.… ▽ More Recent observations suggest that planetary engulfment by a giant star may produce radiation that resembles subluminous red novae. We present three-dimensional hydrodynamical simulations of the interaction between an eccentric $5 \,M_J$ giant planet and its $1\,M_\odot$ red-giant host star. The planet's pericenter is initially $60\%$ of the stellar radius and is fully engulfed after tens of orbits. Once inside the stellar envelope, the planet generates pressure disturbances that steepen into shocks, ejecting material from the envelope. We use post-processing to calculate the light curves produced by planetary engulfment. We find that the hot stellar ejecta enhances the stellar luminosity by several orders of magnitude. A prolonged hydrogen recombination plateau appears when the ejecta cools to about $10^4\,\rm{K}$. The late-time rapid dimming of the light curve follows dust formation, which obscures the radiation. For planets with lower eccentricity, the orbital decay proceeds more slowly, although the observable properties remain similar. △ Less

Submitted 29 October, 2025; originally announced October 2025.

Comments: 20 pages, 8 figures, submitted to The Astrophysical Journal

Kinematic, Elemental and Structural Dependences on Metallicity in the Galactic Bulge

Authors: Haoyang Liu, Cuihua Du, Zhongcheng Li, Jian Zhang, Mingji Deng

Abstract: We selected Bulge stars from APOGEE DR17 cross-matched with astrometric data from \textit{Gaia} DR3. Bulge stars were divided into sub-samples with line-of-sight velocity dispersion analyzed and the peaks of MDF were detected by both Gaussian Mixture Models (GMM) and \texttt{scipy.signal.find\_peaks}. GMM is also conducted to kinematically distinguish the metal-poor and metal-rich populations. Ana… ▽ More We selected Bulge stars from APOGEE DR17 cross-matched with astrometric data from \textit{Gaia} DR3. Bulge stars were divided into sub-samples with line-of-sight velocity dispersion analyzed and the peaks of MDF were detected by both Gaussian Mixture Models (GMM) and \texttt{scipy.signal.find\_peaks}. GMM is also conducted to kinematically distinguish the metal-poor and metal-rich populations. Analyses were put on the Bulge stars (including retrograde stars), their elemental abundances, and the [Mg/Mn]-[Al/Fe] plane to investigate potential accreted components. Finally, the shapes (X-shaped/boxy) of Bulge stars with different metallicities were analyzed through least-squares fitting based on the analytical Bulge models. By studying the kinematic, elemental and structural dependences on metallicity for Bulge stars, our findings are concluded as follows: 1. Six peaks are detected in the Bulge MDF, encompassing values reported in previous studies, suggesting a complex composition of Bulge populations. 2. An inversion relationship is well-observed in metal-rich sub-samples, while absent in metal-poor sub-samples. 3. Metal-poor populations exhibit larger dispersions than metal-rich stars (which is also revealed by GMM decomposition), suggesting that metal-rich stars are kinematically coherent. 4. Retrograde stars are confined to $\sim1$ kpc of the Galactic center, with their relative fraction decreasing at higher [Fe/H] -- a trend potentially linked to the ``spin-up'' process of Galactic disks. 5. Metal-rich Bulge stars with [Al/Fe] $<-0.15$ are likely associated with from disk accreted substructure, while all elemental planes exhibit bimodality but Na abundances rise monotonically with metallicity. 6. In general, stars with all metallicities support a boxy profile. △ Less

Submitted 28 October, 2025; originally announced October 2025.

Comments: 12 pages, 10 figures, accepted for publication in A&A

SN 2024iss: A Double-peaked Type IIb Supernova with Evidence of Circumstellar Interaction

Authors: Liyang Chen, Xiaofeng Wang, Qinyu Wu, Moira Andrews, Joseph Farah, Paolo Ochner, Andrea Reguitti, Thomas G. Brink, Jujia Zhang, Cuiying Song, Jialian Liu, Alexei V. Filippenko, David J. Sand, Irene Albanese, Kate D. Alexander, Jennifer Andrews, K. Azalee Bostroem, Yongzhi Cai, Collin Christy, Ali Esamdin, Andrea Farina, Noah Franz, D. Andrew Howell, Brian Hsu, Maokai Hu , et al. (32 additional authors not shown)

Abstract: We present optical, ultraviolet, and X-ray observations of supernova (SN) 2024iss, a Type IIb SN that shows a prominent double-peaked light curve. We modeled the first peak with a semianalytical shock-cooling model and the X-ray emission with a free-free model. We compare the envelope radius and mass-loss rate with other Type IIb SNe to explore the relationships between the progenitor envelope and… ▽ More We present optical, ultraviolet, and X-ray observations of supernova (SN) 2024iss, a Type IIb SN that shows a prominent double-peaked light curve. We modeled the first peak with a semianalytical shock-cooling model and the X-ray emission with a free-free model. We compare the envelope radius and mass-loss rate with other Type IIb SNe to explore the relationships between the progenitor envelope and the circumstellar material (CSM). The shock-cooling peak in the $V$-band light curve reached $M_V = -17.33\pm 0.26$mag, while the $^{56}$Ni-powered second peak attained $M_V = -17.43\pm 0.26$mag. Early spectra show an photospheric velocity of $\sim19,400\,km\,s^{-1}$ at 3.82days from the H$α$ P~Cygni profile. The Balmer lines persist at least +87 days after the explosion, characterizing hydrogen-rich ejecta. Modeling the first light-curve peak suggests an extended envelope with a mass of $0.11\pm0.04\,M_{\odot}$ and a radius of $244\pm43~R_{\odot}$. Fitting the second light-curve peak with an Arnett-like model indicates a typical $^{56}$Ni mass of $ 0.117\pm0.013~M_{\odot}$ and a relatively low ejecta mass of $1.272\pm0.343\,M_{\odot}$. X-ray observations reveal bright thermal bremsstrahlung emission and indicate a mass-loss rate of $1.6\times10^{-5}\ M_{\odot} \ \rm{yr}^{-1}$. SN 2024iss occupies a transitional position between the two subclasses of extended (eIIb) and compact (cIIb) Type IIb SNe. Its envelope radius and pre-explosion mass-loss rate appear to be correlated as theoretically predicted. The observational properties of SN 2024iss are compatible with a binary interaction scenario being the dominant mechanism for envelope stripping. Furthermore, the low column density of neutral hydrogen suggests a compact CSM with an outer radius of $\lesssim1.3\times10^{14}$ cm, indicating that the progenitor star experienced eruptive mass loss within $\sim4\,yr$ of its terminal explosion. △ Less

Submitted 27 October, 2025; originally announced October 2025.

Comments: 24 pages, 14 figures, submitted to A&A

SN2017ckj: A linearly declining Type IIb supernova with a relatively massive hydrogen envelope

Authors: L. -H. Li, S. Benetti, Y. -Z. Cai, B. Wang, A. Pastorello, N. Elias-Rosa, A. Reguitti, L. Borsato, E. Cappellaro, A. Fiore, M. Fraser, M. Gromadzki, J. Harmanen, J. Isern, T. Kangas, E. Kankare, P. Lundqvist, S. Mattila, P. Ochner, Z. -H. Peng, T. M. Reynolds, I. Salmaso, S. Srivastav, M. D. Stritzinger, L. Tomasella , et al. (4 additional authors not shown)

Abstract: We present optical observations of the Type IIb supernova (SN) 2017ckj, covering approximately 180 days after the explosion. Its early-time multi-band light curves display no clear evidence of a shock-cooling tail, resembling the behavior of SN2008ax. The $V$-band light curve exhibits a short rise time of about 5 days and reaches an absolute fitted peak magnitude of… ▽ More We present optical observations of the Type IIb supernova (SN) 2017ckj, covering approximately 180 days after the explosion. Its early-time multi-band light curves display no clear evidence of a shock-cooling tail, resembling the behavior of SN2008ax. The $V$-band light curve exhibits a short rise time of about 5 days and reaches an absolute fitted peak magnitude of $M_{\rm V}=-18.49\pm0.18\mathrm{mag}$. The late-time multi-band light curves reveal a linear decline. We modelled the bolometric light curve of SN2017ckj to constrain the progenitor and the explosion parameters. We estimated a total mass of $\rm ^{56}Ni$ synthesized by SN2017ckj of $M_{\rm Ni} = 0.21^{+0.05}_{-0.03}\ M_\odot$, with a massive H-rich envelope of $M_{\rm env} = 0.4^{+0.1}_{-0.1}\ M_\odot$. Both the $\rm ^{56}Ni$ mass and the envelope mass of SN2017ckj are higher than those of typical SNe IIb, in agreement with its peculiar light curve evolution. The early-time spectra of SN2017ckj are dominated by a blue continuum, accompanied by narrow $\rm H_α$ and \Heii emission lines. The earliest spectrum exhibits flash ionization features, from which we estimated a progenitor mass-loss rate of $\sim 3\times10^{-4}M_\odot \mathrm{yr}^{-1}$. At later epochs, the spectra develop broad P-Cygni profiles and become increasingly similar to those of SNe IIb, especially SN2018gk. The late-time spectrum at around 139 days does not show a distinct decline in the strength of $\rm H_α$ emission profile, also indicating a relatively massive envelope of its progenitor. Aside from the $\rm H_α$ feature, the nebular spectrum exhibits prominent emission lines of \Oi, \Caii, [\Caii], and \Mgi], which are consistent with the prototypical SN1993J. △ Less

Submitted 16 December, 2025; v1 submitted 27 October, 2025; originally announced October 2025.

Comments: 19 pages, 15 figures, published in A&A

Synergy between CSST and third-generation gravitational-wave detectors: Inferring cosmological parameters using cross-correlation of dark sirens and galaxies

Authors: Ya-Nan Du, Ji-Yu Song, Yichao Li, Shang-Jie Jin, Ling-Feng Wang, Jing-Fei Zhang, Xin Zhang

Abstract: Gravitational-wave (GW) events are generally believed to originate in galaxies and can thus serve, like galaxies, as tracers of the universe's large-scale structure. In GW observations, waveform analysis provides direct measurements of luminosity distances; however, the redshifts of GW sources cannot be determined due to the mass-redshift degeneracy. By cross-correlating GW events with galaxies, o… ▽ More Gravitational-wave (GW) events are generally believed to originate in galaxies and can thus serve, like galaxies, as tracers of the universe's large-scale structure. In GW observations, waveform analysis provides direct measurements of luminosity distances; however, the redshifts of GW sources cannot be determined due to the mass-redshift degeneracy. By cross-correlating GW events with galaxies, one can establish a correspondence between luminosity distance and redshift shells, enabling cosmological inference. In this work, we explore the scientific potential of cross-correlating GW sources detected by third-generation (3G) ground-based GW detectors with the photometric redshift survey of the China Space Station Survey Telescope (CSST). We find that the constraint precisions of the Hubble constant and the matter density parameter can reach $1.04\%$ and $2.04\%$, respectively. The GW clustering bias parameters $A_{\rm GW}$ and $γ$ can be constrained to $1.52\%$ and $4.67\%$, respectively. These results highlight the significant potential of the synergy between CSST and 3G ground-based GW detectors in constraining cosmological models and probing GW source formation channels using cross-correlation of dark sirens and galaxies. △ Less

Submitted 24 October, 2025; originally announced October 2025.

Comments: 15 pages, 7 figures

Discovery of a Debris Disk Around TWA 20

Authors: Skyler Palatnick, Maxwell A. Millar-Blanchaer, Jingwen Zhang, Kellen Lawson, Briley L. Lewis, Katie A. Crotts, Aarynn L. Carter, Beth Biller, Julien H. Girard, Sebastian Marino, Raphael Bendahan-West, Giovanni M. Strampelli, Andrew D. James, Klaus Subbotina Stephenson, Rodrigo Ferrer-Chavez, Mark Booth, Ben J. Sutlieff, Aniket Sanghi, Clemence Fontanive, Emily Rickman, Isabel Rebollido, Kielan Hoch, William O. Balmer

Abstract: We report the discovery of a debris disk surrounding the M3 star, TWA 20, revealed by JWST coronagraphic observations using the Near-infrared Camera (NIRCam). With reference-star differential imaging (RDI), we resolve the disk in scattered light in the F200W filter at a high signal-to-noise ratio and in the F444W filter at a low signal-to-noise ratio. The disk morphology and orientation are charac… ▽ More We report the discovery of a debris disk surrounding the M3 star, TWA 20, revealed by JWST coronagraphic observations using the Near-infrared Camera (NIRCam). With reference-star differential imaging (RDI), we resolve the disk in scattered light in the F200W filter at a high signal-to-noise ratio and in the F444W filter at a low signal-to-noise ratio. The disk morphology and orientation are characterized via a forward modeling approach, where we determine a radius of 64.7-6.5+6.2 AU and an inclination of 70.1-3.3+2.5 deg. Utilizing our forward model, we improve the fidelity of the debris disk image using model-constrained RDI (MCRDI). The newly discovered disk is one of only 6 disks detected in scattered light that orbit M dwarf stars; it is the third largest of the 6 resolved M dwarf disks and orbits the third faintest host star. The detection of this disk exemplifies the sensitivity of JWST to debris disks around low-luminosity host stars, which have historically been difficult to detect because these disks are cool and dim. We identify a nebulous structure that cannot be explained by an axisymmetric disk. A search for companions in the TWA 20 system yields no candidates. △ Less

Submitted 23 October, 2025; originally announced October 2025.

Comments: 16 pages, 11 figures, accepted for publication in ApJ

Starspots as the origin of ultrafast drifting radio bursts from an active M dwarf

Authors: Jiale Zhang, Hui Tian, Stefano Bellotti, Tianqi Cang, Joseph R. Callingham, Harish K. Vedantham, Bin Chen, Sijie Yu, Philippe Zarka, Corentin K. Louis, Peng Jiang, Hongpeng Lu, Yang Gao, Jinghai Sun, Hengqian Gan, Hui Li, Chun Sun, Zheng Lei, Menglin Huang

Abstract: Detecting coherent radio bursts from nearby M dwarfs provides opportunities for exploring their magnetic activity and interaction with orbiting exoplanets. However, it remains uncertain if the emission is related to flare-like activity similar to the Sun or magnetospheric process akin to magnetized planets. Using observations (1.0 - 1.5 GHz) taken by the Five-hundred-meter Aperture Spherical radio… ▽ More Detecting coherent radio bursts from nearby M dwarfs provides opportunities for exploring their magnetic activity and interaction with orbiting exoplanets. However, it remains uncertain if the emission is related to flare-like activity similar to the Sun or magnetospheric process akin to magnetized planets. Using observations (1.0 - 1.5 GHz) taken by the Five-hundred-meter Aperture Spherical radio Telescope, we found a type of millisecond-scale radio bursts with exceptionally high frequency drift rates ($\sim 8\;\rm{GHz\;s^{-1}}$) from an active M dwarf, AD Leo. The ultrafast drift rates point to a source region with a notably low magnetic scale height ($<0.15\; r_\star$, $r_\star$ as the stellar radius), a feature not expected in a commonly assumed dipole-like global field but highly possible in localized strong-field structures, i.e. starspots. Our findings suggest that a concentrated magnetic field above starspots could be responsible for some of the most intense radio bursts from M dwarfs, supporting a solar-like electron acceleration mechanism. △ Less

Submitted 20 October, 2025; originally announced October 2025.

Comments: Published on Science Advances, the authors' version

Journal ref: Science Advances (2025) 11, 42

From Stars to Waves: Non-deterministic Inference of Microlensed Gravitational Waves

Authors: Zhaoqi Su, Xikai Shan, Zhenwei Lyu, Junyao Zhang, Yebin Liu, Shude Mao, Huan Yang

Abstract: Strongly lensed gravitational waves may pass through the stellar field of a lensing galaxy with additional modulations (on both phase and amplitude) due to gravitational microlensing effect of stars/remnants near the line of sight. These microlensed waveforms depend on the mass and location of thousands or more most relevant stars, so that their deterministic reconstruction from the data is comput… ▽ More Strongly lensed gravitational waves may pass through the stellar field of a lensing galaxy with additional modulations (on both phase and amplitude) due to gravitational microlensing effect of stars/remnants near the line of sight. These microlensed waveforms depend on the mass and location of thousands or more most relevant stars, so that their deterministic reconstruction from the data is computationally prohibitive. We classify the detection and parameter estimation of such events as non-deterministic inference problem and propose a solution with the implementation of normalizing flows. As a first step, we show that $8\%$ of microlensed events can be detected with significance $\ge 3 σ$ in the third generation era, with the chosen microlensing parameters correlated with the density of the underlying stellar field. This approach opens the door to probing microlensing effects and the properties of the underlying stellar fields. A similar construction may also be applied to other non-deterministic inference problems, such as detecting post-merger gravitational waves from binary neutron star coalescence and signals from core-collapse supernovae. △ Less

Submitted 19 October, 2025; originally announced October 2025.

Comments: 19 pages, 11 figures, comments are welcome!

A Practical Framework for Estimating the Repetition Likelihood of Fast Radio Bursts from Spectral Morphology

Authors: Wan-Peng Sun, Yong-Kun Zhang, Ji-Guo Zhang, Xiaohui Liu, Yichao Li, Fu-Wen Zhang, Wan-Ting Hou, Jing-Fei Zhang, Xin Zhang

Abstract: The repeating behavior of fast radio bursts (FRBs) is regarded as a key clue to understanding their physical origin, yet reliably distinguishing repeaters from apparent non-repeaters with current observations remains challenging. Here we propose a physically interpretable and practically quantifiable classification framework based on spectral morphology. Using dimensionality reduction, clustering,… ▽ More The repeating behavior of fast radio bursts (FRBs) is regarded as a key clue to understanding their physical origin, yet reliably distinguishing repeaters from apparent non-repeaters with current observations remains challenging. Here we propose a physically interpretable and practically quantifiable classification framework based on spectral morphology. Using dimensionality reduction, clustering, and feature-importance analysis, we identify the spectral running $r$ and spectral index $γ$ as the most critical parameters for distinguishing repeaters from apparent non-repeaters in the CHIME/FRB sample. In the $γ$-$r$ space, repeaters preferentially occupy regions with steeper, narrower-band spectra, whereas non-repeaters cluster in flatter, broader-band regions, resulting in a clear density separation. We further construct an empirical probability map in the $γ$-$r$ space, showing a clear gradient of repetition likelihood, from $\sim 65\%$ in the high-repetition region to $\sim 5\%$ in the low-repetition region. Combining this with Gaussian Mixture Model posterior analysis, we identify several apparent non-repeaters with high inferred repetition probability, recommending them as priority targets for future monitoring. This framework provides a simple and generalizable tool for assessing repeatability in the CHIME/FRB sample and highlights the diagnostic power of spectral morphology in unveiling FRB origins. △ Less

Submitted 17 October, 2025; originally announced October 2025.

Comments: 15 pages, 4 figures