Showing 1–50 of 1,196 results for author: Zhang, B

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

Explosions in the Empty: A Survey of Transients in Local Void Galaxies

Authors: Suo-Ning Wang, Bin-Bin Zhang, Rubén García Benito

Abstract: We present a systematic analysis of transient astrophysical events -- including supernovae (SNe), gamma-ray bursts (GRBs), and fast radio bursts (FRBs) -- in void and non-void galaxies within the local universe ($0.005 < z < 0.05$). Cosmic voids, defined by low galaxy densities and characterized by minimal environmental interactions, offer a natural laboratory for isolating the impact of large-sca… ▽ More We present a systematic analysis of transient astrophysical events -- including supernovae (SNe), gamma-ray bursts (GRBs), and fast radio bursts (FRBs) -- in void and non-void galaxies within the local universe ($0.005 < z < 0.05$). Cosmic voids, defined by low galaxy densities and characterized by minimal environmental interactions, offer a natural laboratory for isolating the impact of large-scale underdensities on stellar evolution and transient production. Using multi-wavelength data from the Sloan Digital Sky Survey, the Sternberg Astronomical Institute Supernova Catalogue, and high-energy space observatories, we compare transient occurrence rates and host galaxy properties across environments. We find that core-collapse supernovae (CCSNe) are significantly more common in void galaxies, indicating that massive star formation remains active in underdense regions. In contrast, Type Ia supernovae are less frequent in voids, consistent with a scarcity of older stellar populations. Notably, we identify a short-duration GRB hosted by a void galaxy, demonstrating that compact object mergers can occur in isolated environments. Additionally, we find no FRBs associated with void galaxies. Taken together, these results show that cosmic voids exert a measurable influence on the star formation history of galaxies and hence on the production of transients. △ Less

Submitted 19 November, 2025; originally announced November 2025.

Comments: 52 pages, 4 figures, 6 tables

Detection of disk-jet co-precession in a tidal disruption event

Authors: Yanan Wang, Zikun Lin, Linhui Wu, Weihua Lei, Shuyuan Wei, Shuang-Nan Zhang, Long Ji, Santiago del Palacio, Ranieri D. Baldi, Yang Huang, Jifeng Liu, Bing Zhang, Aiyuan Yang, Rurong Chen, Yangwei Zhang, Ailing Wang, Lei Yang, Panos Charalampopoulos, David R. A. Williams-Baldwin, Zhu-Heng Yao, Fu-Guo Xie, Defu Bu, Hua Feng, Xinwu Cao, Hongzhou Wu , et al. (24 additional authors not shown)

Abstract: Theories and simulations predict that intense spacetime curvature near black holes bends the trajectories of light and matter, driving disk and jet precession under relativistic torques. However, direct observational evidence of disk-jet co-precession remains elusive. Here, we report the most compelling case to date: a tidal disruption event (TDE) exhibiting unprecedented 19.6-day quasi-periodic v… ▽ More Theories and simulations predict that intense spacetime curvature near black holes bends the trajectories of light and matter, driving disk and jet precession under relativistic torques. However, direct observational evidence of disk-jet co-precession remains elusive. Here, we report the most compelling case to date: a tidal disruption event (TDE) exhibiting unprecedented 19.6-day quasi-periodic variations in both X-rays and radio, with X-ray amplitudes exceeding an order of magnitude. The nearly synchronized X-ray and radio variations suggest a shared mechanism regulating the emission regions. We demonstrate that a disk-jet Lense-Thirring precession model successfully reproduces these variations while requiring a low-spin black hole. This study uncovers previously uncharted short-term radio variability in TDEs, highlights the transformative potential of high-cadence radio monitoring, and offers profound insights into disk-jet physics. △ Less

Submitted 16 November, 2025; originally announced November 2025.

Comments: 76 pages, 13 figures (initial submission; in press at Science Advances)

Mock Observations for the CSST Mission: Main Surveys--the Stray Light

Authors: Xian Jing-Tian, Lin Lin, Fang Yue-Dong, Zhang Xin, Xu You-Hua, Meng Xian-Min, Tian Hao, Zhang Tian-Yi, Ban Zhang, Li Guo-Liang, Xu Shu-Yan, Wang Wei

Abstract: Stray light significantly influences the detection capabilities of astronomical telescopes. The actual stray-light level during observations depends not only on the telescope's inherent stray-light suppression capability but also on its operational orbit conditions. Accurate estimation of stray-light levels is crucial for assessing image quality and performing realistic scientific simulations. To… ▽ More Stray light significantly influences the detection capabilities of astronomical telescopes. The actual stray-light level during observations depends not only on the telescope's inherent stray-light suppression capability but also on its operational orbit conditions. Accurate estimation of stray-light levels is crucial for assessing image quality and performing realistic scientific simulations. To rapidly estimate stray-light levels under realistic, complex operational conditions, we developed an analytical model tailored to the China Space Station Telescope (CSST). Our model simulates stray-light backgrounds generated by off-field sources such as moonlight, starlight, and earthshine, incorporating the effects of zodiacal light, as well as scattering and ghost images induced by bright in-field stars. The proposed method allows quick and accurate evaluation of stray-light conditions, facilitating both image simulation and observational scheduling. △ Less

Submitted 10 November, 2025; originally announced November 2025.

Formation Channels of Magnetars

Authors: Rui-Chong Hu, Bing Zhang

Abstract: The formation channels of magnetars remain an open question. Although core collapse supernovae of isolated massive stars are important, binary interactions -- such as tidal interaction, common envelope evolution, and stellar mergers -- may also play a significant role in making magnetars. Understanding the relative contributions of these channels is crucial for linking magnetars to their observed… ▽ More The formation channels of magnetars remain an open question. Although core collapse supernovae of isolated massive stars are important, binary interactions -- such as tidal interaction, common envelope evolution, and stellar mergers -- may also play a significant role in making magnetars. Understanding the relative contributions of these channels is crucial for linking magnetars to their observed properties and host environments. In this paper, we investigate potential magnetar formation channels using population synthesis simulations, considering both single-star and isolated binary system evolution. By conducting simulations with different parameters, we compare the effects of various evolution processes on magnetar formation. Additionally, we study the delay times and kick velocities across all formation channels, analyze the orbital properties and companion types of surviving magnetar binaries. We find that the majority of magnetars are observed as single objects ($\geq 90\%$), although a large fraction of them were originally in binary systems and experienced either kick disruption or merger. Surviving binaries are most likely to host main-sequence companions and exhibit different distributions of eccentricities due to different supernova mechanisms. These findings show the critical role of binary evolution in magnetar formation and provide predictions for the properties of magnetar populations that can be tested with future observations. △ Less

Submitted 9 November, 2025; originally announced November 2025.

Comments: 18 pages, 12 figures, submitted

The Initial mass function of field stars with mass $\leq$ 1 $M_{\odot}$ varies with metallicity

Authors: Dan Qiu, Chao Liu, Jennifer A. Johnson, Jiadong Li, Bo Zhang

Abstract: We investigated a volume-limited sample of LAMOST main-sequence stars with masses from 0.25 to 1 $M_{\odot}$ and distances of 150-350 pc to explore how the stellar initial mass function (IMF) varies with metallicity. We corrected the spectroscopic selection function by comparing the stellar number densities with the photometric ones at the same colour and magnitude. From these corrected number den… ▽ More We investigated a volume-limited sample of LAMOST main-sequence stars with masses from 0.25 to 1 $M_{\odot}$ and distances of 150-350 pc to explore how the stellar initial mass function (IMF) varies with metallicity. We corrected the spectroscopic selection function by comparing the stellar number densities with the photometric ones at the same colour and magnitude. From these corrected number density distributions, we derived IMFs for each metallicity sub-samples. Fitting a broken power-law function in each IMF with a fixed break point at 0.525 $M_{\odot}$, we found the power-law indices increase with [Fe/H] for both mass regimes: $α_1$ (mass $\leq$ 0.525 $M_{\odot}$) rises from 0.54 $\pm$ 0.21 to 1.40 $\pm$ 0.07 and $α_2$ (mass>0.525 $M_{\odot}$) grows from 1.40 $\pm$ 0.16 to 1.86 $\pm$ 0.04 as [Fe/H] varies from -1 to +0.5 dex. It demonstrates that low-mass stars make up a larger fraction in metal-rich environments than in metal-poor ones. We performed simulations to assess the impact of unresolved binaries on the IMF power-law indices. After correction, the binary-adjusted $α$ values retained a similar metallicity-dependent trend. Furthermore, by examining the IMF of the aggregate sample, we found the corrected indices ($α_{\rm{1,corr}} = 1.48 \pm 0.03$ , $α_{\rm{2,corr}} = 2.17 \pm 0.03$) are consistent with Kroupa's IMF values ($α_1 = 1.3 \pm 0.5$ and $α_2 = 2.3 \pm 0.3$). Finally, we verified the robustness of our results by testing different break points and mass bin sizes, confirming that the IMF's dependence on [Fe/H] remains consistent. △ Less

Submitted 6 November, 2025; originally announced November 2025.

Comments: 12 pages, 13 figures

First Associated Neutrino Search for a Failed Supernova Candidate with Super-Kamiokande

Authors: F. Nakanishi, K. Abe, S. Abe, Y. Asaoka, M. Harada, Y. Hayato, K. Hiraide, K. Hosokawa, T. H. Hung, K. Ieki, M. Ikeda, J. Kameda, Y. Kanemura, Y. Kataoka, S. Miki, S. Mine, M. Miura, S. Moriyama, M. Nakahata, S. Nakayama, Y. Noguchi, G. Pronost, K. Sato, H. Sekiya, M. Shiozawa , et al. (221 additional authors not shown)

Abstract: In 2024, a failed supernova candidate, M31-2014-DS1, was reported in the Andromeda galaxy (M31), located at a distance of approximately 770 kpc. In this paper, we search for neutrinos from this failed supernova using data from Super-Kamiokande (SK). Based on the estimated time of black hole formation inferred from optical and infrared observations, we define a search window for neutrino events in… ▽ More In 2024, a failed supernova candidate, M31-2014-DS1, was reported in the Andromeda galaxy (M31), located at a distance of approximately 770 kpc. In this paper, we search for neutrinos from this failed supernova using data from Super-Kamiokande (SK). Based on the estimated time of black hole formation inferred from optical and infrared observations, we define a search window for neutrino events in the SK data. Using this window, we develop a dedicated analysis method for failed supernovae and apply it to M31-2014-DS1, by conducting a cluster search using the timing and energy information of candidate events. No significant neutrino excess is observed within the search region. Consequently, we place an upper limit on the electron antineutrino luminosity from M31-2014-DS1 and discuss its implications for various failed SN models and their neutrino emission characteristics. Despite the 18 MeV threshold adopted to suppress backgrounds, the search remains sufficiently sensitive to constrain the Shen-TM1 EOS, yielding a 90% confidence level upper limit of 1.76 \times 10^{53} erg on the electron antineutrino luminosity, slightly above the expected value of 1.35 \times 10^{53} erg. △ Less

Submitted 5 November, 2025; v1 submitted 5 November, 2025; originally announced November 2025.

Comments: 11 pages, 4 figures, and 1 table

Search for Diffuse Supernova Neutrino Background with 956.2 days of Super-Kamiokande Gadolinium Dataset

Authors: K. Abe, S. Abe, Y. Asaoka, M. Harada, Y. Hayato, K. Hiraide, K. Hosokawa, T. H. Hung, K. Ieki, M. Ikeda, J. Kameda, Y. Kanemura, Y. Kataoka, S. Miki, S. Mine, M. Miura, S. Moriyama, M. Nakahata, S. Nakayama, Y. Noguchi, G. Pronost, K. Sato, H. Sekiya, R. Shinoda, M. Shiozawa , et al. (223 additional authors not shown)

Abstract: We report the search result for the Diffuse Supernova Neutrino Background (DSNB) in neutrino energies beyond 9.3~MeV in the gadolinium-loaded Super-Kamiokande (SK) detector with $22,500\times956.2$$~\rm m^3\cdot day$ exposure. %$22.5{\rm k}\times956.2$$~\rm m^3\cdot day$ exposure. Starting in the summer of 2020, SK introduced 0.01\% gadolinium (Gd) by mass into its ultra-pure water to enhance the… ▽ More We report the search result for the Diffuse Supernova Neutrino Background (DSNB) in neutrino energies beyond 9.3~MeV in the gadolinium-loaded Super-Kamiokande (SK) detector with $22,500\times956.2$$~\rm m^3\cdot day$ exposure. %$22.5{\rm k}\times956.2$$~\rm m^3\cdot day$ exposure. Starting in the summer of 2020, SK introduced 0.01\% gadolinium (Gd) by mass into its ultra-pure water to enhance the neutron capture signal, termed the SK-VI phase. This was followed by a 0.03\% Gd-loading in 2022, a phase referred to as SK-VII. We then conducted a DSNB search using 552.2~days of SK-VI data and 404.0~days of SK-VII data through September 2023. This analysis includes several new features, such as two new machine-learning neutron detection algorithms with Gd, an improved atmospheric background reduction technique, and two parallel statistical approaches. No significant excess over background predictions was found in a DSNB spectrum-independent analysis, and 90\% C.L. upper limits on the astrophysical electron anti-neutrino flux were set. Additionally, a spectral fitting result exhibited a $\sim1.2σ$ disagreement with a null DSNB hypothesis, comparable to a previous result from 5823~days of all SK pure water phases. △ Less

Submitted 3 November, 2025; originally announced November 2025.

The Advanced X-ray Imaging Satellite Community Science Book

Authors: Michael Koss, Nafisa Aftab, Steven W. Allen, Roberta Amato, Hongjun An, Igor Andreoni, Timo Anguita, Riccardo Arcodia, Thomas Ayres, Matteo Bachetti, Maria Cristina Baglio, Arash Bahramian, Marco Balboni, Ranieri D. Baldi, Solen Balman, Aya Bamba, Eduardo Banados, Tong Bao, Iacopo Bartalucci, Antara Basu-Zych, Rebeca Batalha, Lorenzo Battistini, Franz Erik Bauer, Andy Beardmore, Werner Becker , et al. (373 additional authors not shown)

Abstract: The AXIS Community Science Book represents the collective effort of more than 500 scientists worldwide to define the transformative science enabled by the Advanced X-ray Imaging Satellite (AXIS), a next-generation X-ray mission selected by NASA's Astrophysics Probe Program for Phase A study. AXIS will advance the legacy of high-angular-resolution X-ray astronomy with ~1.5'' imaging over a wide 24'… ▽ More The AXIS Community Science Book represents the collective effort of more than 500 scientists worldwide to define the transformative science enabled by the Advanced X-ray Imaging Satellite (AXIS), a next-generation X-ray mission selected by NASA's Astrophysics Probe Program for Phase A study. AXIS will advance the legacy of high-angular-resolution X-ray astronomy with ~1.5'' imaging over a wide 24' field of view and an order of magnitude greater collecting area than Chandra in the 0.3-12 keV band. Combining sharp imaging, high throughput, and rapid response capabilities, AXIS will open new windows on virtually every aspect of modern astrophysics, exploring the birth and growth of supermassive black holes, the feedback processes that shape galaxies, the life cycles of stars and exoplanet environments, and the nature of compact stellar remnants, supernova remnants, and explosive transients. This book compiles over 140 community-contributed science cases developed by five Science Working Groups focused on AGN and supermassive black holes, galaxy evolution and feedback, compact objects and supernova remnants, stellar physics and exoplanets, and time-domain and multi-messenger astrophysics. Together, these studies establish the scientific foundation for next-generation X-ray exploration in the 2030s and highlight strong synergies with facilities of the 2030s, such as JWST, Roman, Rubin/LSST, SKA, ALMA, ngVLA, and next-generation gravitational-wave and neutrino networks. △ Less

Submitted 31 October, 2025; originally announced November 2025.

Comments: 595 pages, 225 figures

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.

Fast-Cooling Synchrotron Prompt Emission from Internal Shocks in GRB 241030A

Authors: Varun, Bin-Bin Zhang, Xiao-Hong Zhao, Jun Yang, Run-Chao Chen, Vikas Chand

Abstract: We present a time-resolved, joint Swift-Fermi spectral study of GRB 241030A (z=1.411) that cleanly isolates the synchrotron origin of its prompt emission and favors a matter-dominated, internal-shock scenario. The light curve shows two episodes separated by a quiescent gap. Episode I (0-45 s) is well described by a single power law with photon index $\simeq -3/2$, consistent with the fast-cooling… ▽ More We present a time-resolved, joint Swift-Fermi spectral study of GRB 241030A (z=1.411) that cleanly isolates the synchrotron origin of its prompt emission and favors a matter-dominated, internal-shock scenario. The light curve shows two episodes separated by a quiescent gap. Episode I (0-45 s) is well described by a single power law with photon index $\simeq -3/2$, consistent with the fast-cooling synchrotron slope below the peak. Episode II (100-200 s), exhibits two robust spectral breaks: a low-energy break at $E_{b}$$\sim$$2-3$ keV that remains nearly constant in time, and a spectral peak $E_{p}$ that tracks the flux within pulses but steps down between them. The photon indices below and above $E_{b}$ cluster around -2/3 and -3/2, respectively, as expected for fast-cooling synchrotron emission. The burst displays an unusually small (consistent with zero) spectral lag across GBM bands. At later times ($\geq 230$ s), the spectrum softens toward $\sim-2.7$, as expected when the observing band lies above both $ν_m$ and $ν_c$. These behaviors are difficult to reconcile with a globally magnetized outflow with a decaying field, which naturally produces hard-to-soft Ep evolution, growing $ν_c$, and appreciable lags. By contrast, internal shocks with a roughly steady effective magnetic field and a time-variable minimum electron Lorentz factor (equivalently, e.g., a varying fraction of accelerated electrons simultaneously account for (i) the stable $E_{b}$, (ii) the intensity-tracking yet step-down $E_{p}$, (iii) the canonical -2/3 and -3/2 slopes, and (iv) the near-zero lag. △ Less

Submitted 28 October, 2025; originally announced October 2025.

Comments: 16 pages, 8 Figures, 3 Tables. Submitted to APJ

Investigating Production of TeV-scale Muons in Extensive Air Shower at 2400 Meters Underground

Authors: Xinshun Zhang, Shaomin Chen, Wei Dou, Haoyang Fu, Lei Guo, Ziyi Guo, XiangPan Ji, Jianmin Li, Jinjing Li, Bo Liang, Ye Liang, Qian Liu, Wentai Luo, Ming Qi, Wenhui Shao, Haozhe Sun, Jian Tang, Yuyi Wang, Zhe Wang, Changxu Wei, Jun Weng, Yiyang Wu, Benda Xu, Chuang Xu, Tong Xu , et al. (8 additional authors not shown)

Abstract: The China Jinping Underground Laboratory, characterized by a vertical rock overburden of 2,400 m, provides an exceptionally effective shield against cosmic muons with energies below 3 TeV. The surviving high-energy muons, produced as part of extensive air showers, open a unique observational window into primary cosmic rays with energies ranging from tens of TeV up to the PeV scale and beyond. This… ▽ More The China Jinping Underground Laboratory, characterized by a vertical rock overburden of 2,400 m, provides an exceptionally effective shield against cosmic muons with energies below 3 TeV. The surviving high-energy muons, produced as part of extensive air showers, open a unique observational window into primary cosmic rays with energies ranging from tens of TeV up to the PeV scale and beyond. This distinctive feature also enables detailed studies of the earliest stages of shower development. Using 1,338.6 live days of data collected with a one-ton prototype detector for the Jinping Neutrino Experiment, we measured the underground muon flux originating from air showers. The results show discrepancies of about 40%, corresponding to a significance of more than 5.5$σ$, relative to predictions from several leading hadronic interaction models. We interpret these findings from two complementary perspectives: (i) by adopting the expected cosmic ray spectra, we constrain the modeling of the initial hadronic interactions in air showers; and (ii) by assuming specific hadronic interaction models, we infer the mass composition of cosmic rays, and our data favor a lighter component in the corresponding energy range. Our study demonstrates the potential of deep underground laboratories to provide new experimental insights into cosmic rays. △ Less

Submitted 18 October, 2025; originally announced October 2025.

Comments: 7 pages; 5 figures

Exploring the connection between compact object mergers and fast X-ray transients: The cases of LXT 240402A & EP250207b

Authors: R. L. Becerra, Yu-Han Yang, Eleonora Troja, Massine El Kabir, Simone Dichiara, Niccolò Passaleva, Brendan O'Connor, Roberto Ricci, Chris Fryer, Lei Hu, Qinyu Wu, Muskan Yadav, Alan M. Watson, Anastasia Tsvetkova, Camila Angulo-Valdez, María D. Caballero-García, Alberto J. Castro-Tirado, C. C. Cheung, Dmitry Frederiks, Maria Gritsevich, J. E. Grove, M. Kerr, William H. Lee, Alexandra L. Lysenko, Margarita Pereyra Talamantes , et al. (7 additional authors not shown)

Abstract: The connection between compact object mergers and some extragalactic fast X-ray transients (FXRTs) has long been hypothesized, but never ultimately established. In this work, we investigate two FXRTs, the LEIA X-ray Transient LXT 240402A and the Einstein Probe EP250207b, whose precise positions lie close to nearby ($z\!\lesssim\!0.1$) quiescent galaxies with negligible probability of chance coinci… ▽ More The connection between compact object mergers and some extragalactic fast X-ray transients (FXRTs) has long been hypothesized, but never ultimately established. In this work, we investigate two FXRTs, the LEIA X-ray Transient LXT 240402A and the Einstein Probe EP250207b, whose precise positions lie close to nearby ($z\!\lesssim\!0.1$) quiescent galaxies with negligible probability of chance coincidence, identifying them as particularly promising cases of merger-driven explosions in the local Universe. We used Chandra to derive accurate localizations for both events and secure otherwise ambiguous associations with their optical counterparts. Deep optical and near-infrared observations with VLT, GTC, and LBT were performed to characterize the surrounding environment and search for kilonova emission, the hallmark of neutron star mergers. Complementary early-time X-ray monitoring with Swift and Einstein Probe was used to constrain the non-thermal afterglow. We find that both FXRTs remain compatible with a compact binary merger progenitor, which produced low-mass ejecta and kilonova emission subdominant to the afterglow. However, alternative explanations such as a distant ($z\!\gtrsim\!1$) core-collapse supernova cannot be conclusively ruled out. △ Less

Submitted 17 November, 2025; v1 submitted 14 October, 2025; originally announced October 2025.

Comments: Resubmitted to A&A after minor comments

A Giant Peanut-shaped Ultra-High-Energy Gamma-Ray Emitter Off the Galactic Plane

Authors: Zhen Cao, Felix Aharonian, Yunxiang Bai, Yiwei Bao, Denis Bastieri, Xiaojun Bi, YuJiang Bi, Mr Bian WenYi, A. Butkevich, Chengmiao Cai, Wenyu Cao, Zhe Cao, Jin Chang, Jinfan Chang, Mr Aming Chen, Ensheng Chen, Mr Guo-Hai Chen, Mr Huaxi Chen, Liang Chen, Long Chen, Mingjun Chen, Mali Chen, Qihui Chen, Shi Chen, Suhong Chen , et al. (291 additional authors not shown)

Abstract: Ultra-high-energy (UHE), exceeding 100 TeV (10^12 electronvolts), γ-rays manifests extreme particle acceleration in astrophysical sources. Recent observations by γ-ray telescopes, particularly by the Large High Altitude Air Shower Observatory (LHAASO), have revealed a few tens of UHE sources, indicating numerous Galactic sources capable of accelerating particles to PeV (10^15 electronvolts) energi… ▽ More Ultra-high-energy (UHE), exceeding 100 TeV (10^12 electronvolts), γ-rays manifests extreme particle acceleration in astrophysical sources. Recent observations by γ-ray telescopes, particularly by the Large High Altitude Air Shower Observatory (LHAASO), have revealed a few tens of UHE sources, indicating numerous Galactic sources capable of accelerating particles to PeV (10^15 electronvolts) energies. However, discerning the dominant acceleration mechanisms (leptonic versus hadronic), the relative contributions of specific source classes, and the role of particle transport in shaping their observed emission are central goals of modern UHE astrophysics. Here we report the discovery of a giant UHE γ-ray emitter at -17.5° off the Galactic plane - a region where UHE γ-ray sources are rarely found. The emitter exhibits a distinctive asymmetric shape, resembling a giant "Peanut" spanning 0.45° \times 4.6°, indicative of anisotropic particle distribution over a large area. A highly aged millisecond pulsar (MSP) J0218+4232 is the sole candidate accelerator positionally coincident with the Peanut region. Its association with UHE γ-rays extending to 0.7 PeV, if confirmed, would provide the first evidence of a millisecond pulsar powering PeV particles. Such a finding challenges prevailing models, which posit that millisecond pulsars cannot sustain acceleration to PeV energies. The detection reveals fundamental gaps in understanding particle acceleration, cosmic-ray transport, and interstellar magnetic field effects, potentially revealing new PeV accelerator (PeVatron) classes. △ Less

Submitted 25 October, 2025; v1 submitted 8 October, 2025; originally announced October 2025.

A fast powerful X-ray transient from possible tidal disruption of a white dwarf

Authors: D. -Y. Li, W. -D. Zhang, J. Yang, J. -H. Chen, W. Yuan, H. -Q. Cheng, F. Xu, X. -W. Shu, R. -F. Shen, N. Jiang, J. -Z. Zhu, C. Zhou, W. -H. Lei, H. Sun, C. -C. Jin, L. -X. Dai, B. Zhang, Y. -H. Yang, W. -J. Zhang, H. Feng, B. -F. Liu, H. -Y. Zhou, H. -W. Pan, M. -J. Liu, S. Corbel , et al. (57 additional authors not shown)

Abstract: Stars captured by black holes (BHs) can be torn apart by strong tidal forces, producing electromagnetic flares. To date, more than 100 tidal disruption events (TDEs) have been observed, each involving invariably normal gaseous stars whose debris falls onto the BH, sustaining the flares over years. White dwarfs (WDs), which are the most prevalent compact stars and a million times denser--and theref… ▽ More Stars captured by black holes (BHs) can be torn apart by strong tidal forces, producing electromagnetic flares. To date, more than 100 tidal disruption events (TDEs) have been observed, each involving invariably normal gaseous stars whose debris falls onto the BH, sustaining the flares over years. White dwarfs (WDs), which are the most prevalent compact stars and a million times denser--and therefore tougher--than gaseous stars, can only be disrupted by intermediate-mass black holes (IMBHs) of 10^2--10^5 solar masses. WD-TDEs are considered to generate more powerful and short-lived flares, but their evidence has been lacking. Here we report observations of a fast and luminous X-ray transient EP250702a detected by Einstein Probe. Its one-day-long X-ray peak as luminous as 10^(47-49) erg/s showed strong recurrent flares with hard spectra extending to several tens of MeV gamma-rays, as detected by Fermi/GBM and Konus-Wind, indicating relativistic jet emission. The jet's X-ray dropped sharply from 3 x 10^49 erg/s to around 10^44 erg/s within 20 days (10 days in the source rest frame). These characteristics are inconsistent with any known transient phenomena other than a jetted-TDE evolving over an unprecedentedly short timescale, indicating the disruption of a WD by an IMBH. At late times, a new soft component progressively dominates the X-ray spectrum, exhibiting an extreme super-Eddington luminosity, which possibly originates from an accretion disc. WD-TDEs open a new window for investigating the elusive IMBHs and their surrounding stellar environments, and they are prime sources of gravitational waves in the band of space-based interferometers. △ Less

Submitted 22 October, 2025; v1 submitted 30 September, 2025; originally announced September 2025.

Comments: submitted on 19 October 2025

Evidence for a brief appearance of gamma-ray periodicity after a compact star merger

Authors: Run-Chao Chen, Bin-Bin Zhang, Chen-Wei Wang, Wen-Jun Tan, Shao-Lin Xiong, Jun Yang, Yi-Han Iris Yin, Shuang-Nan Zhang, Bing Zhang

Abstract: The product of a compact star merger is usually hypothesized to be a hyperaccreting black hole, typically resulting in a gamma-ray burst (GRB) with a duration shorter than 2~s. However, recent observations of GRB~211211A and GRB~230307A, both arising from compact star mergers, challenge this model due to their minute-long durations. The data from both events are consistent with having a nascent, r… ▽ More The product of a compact star merger is usually hypothesized to be a hyperaccreting black hole, typically resulting in a gamma-ray burst (GRB) with a duration shorter than 2~s. However, recent observations of GRB~211211A and GRB~230307A, both arising from compact star mergers, challenge this model due to their minute-long durations. The data from both events are consistent with having a nascent, rapidly spinning highly magnetized neutron star (a millisecond magnetar) as the merger product and GRB engine, but a smoking gun signature is still missing. Here we report strong but not yet conclusive evidence for the detection of a 909-Hz gamma-ray periodic signal during a brief time window of GRB~230307A, which is consistent with the rotation frequency of such a millisecond magnetar. Notably, the periodic signal appeared for only 160~ms at an epoch coinciding with the transition epoch when the jet emission from the GRB central engine ceased and when the delayed emission from high latitudes started. If this signal is real, the temporal and spectral features of this gamma-ray periodicity can be consistently interpreted as asymmetric mini-jet emission from a dissipating Poynting-flux-dominated jet, as revealed by the energy-dependent light curve data of this burst. △ Less

Submitted 19 September, 2025; originally announced September 2025.

Comments: 43 pages, 10 figures, 2 tables; author's version. Published in Nature Astronomy at https://www.nature.com/articles/s41550-025-02649-w

A misaligned protostellar disk fed by gas streamers in a barred spiral-like massive dense core

Authors: Xiaofeng Mai, Tie Liu, Xunchuan Liu, Bo Zhang, Paul F. Goldsmith, Neal J. Evans II, Qizhou Zhang, Kee-Tae Kim, Dongting Yang, Mika Juvela, Fengwei Xu, Wenyu Jiao, Hongli Liu, Patricio Sanhueza, Guido Garay, Xi Chen, Shengli Qin, Jakobus M. Vorster, Anandmayee Tej, Zhiyuan Ren, Sami Dib, Shanghuo Li, Qiuyi Luo, Jihye Hwang, Prasanta Gorai , et al. (20 additional authors not shown)

Abstract: High-mass stars, born in massive dense cores (MDCs), profoundly impact the cosmic ecosystem through feedback processes and metal enrichment, yet little is known about how MDCs assemble and transfer mass across scales to form high-mass young stellar objects (HMYSOs). Using multi-scale (40-2500 au) observations of an MDC hosting an HMYSO, we identify a coherent dynamical structure analogous to barre… ▽ More High-mass stars, born in massive dense cores (MDCs), profoundly impact the cosmic ecosystem through feedback processes and metal enrichment, yet little is known about how MDCs assemble and transfer mass across scales to form high-mass young stellar objects (HMYSOs). Using multi-scale (40-2500 au) observations of an MDC hosting an HMYSO, we identify a coherent dynamical structure analogous to barred spiral galaxies: three 20,000 au spiral arms feed a 7,500 au central bar, which channels gas to a 2,000 au pseudodisk. Further accretion proceeds through the inner structures, including a Keplerian disk and an inner disk (100 au), which are thought to be driving a collimated bipolar outflow. This is the first time that these multi-scale structures (spiral arms, bar, streamers, envelope, disk, and outflow) have been simultaneously observed as a physically coherent structure within an MDC. Our discovery suggests that well-organized hierarchical structures play a crucial role during the gas accretion and angular momentum build-up of a massive disk. △ Less

Submitted 18 September, 2025; originally announced September 2025.

Revealing Event Rate of Repeating Fast Radio Bursts

Authors: Q. Pan, X. Y. Du, Z. B. Zhang, Y. F. Huang, L. B. Li, G. A. Li

Abstract: How the event rate of fast radio bursts (FRBs) evolves with redshift is a hot topic to explore their cosmological origin and the circum-burst environment. Particularly, it is urgent to know what the difference of event rates between repeating and non-repeating FRBs is. For the first time, we calculate the event rates of repeating FRBs detected by diverse telescopes at frequencies higher/lower than… ▽ More How the event rate of fast radio bursts (FRBs) evolves with redshift is a hot topic to explore their cosmological origin and the circum-burst environment. Particularly, it is urgent to know what the difference of event rates between repeating and non-repeating FRBs is. For the first time, we calculate the event rates of repeating FRBs detected by diverse telescopes at frequencies higher/lower than 1 GHz in this work. Luminosity and redshift are found to be positively correlated with a power law form for both high- and low-frequency FRBs, showing an obvious evolution of luminosity with redshift. Furthermore, we compare the differential luminosity and local event rate distributions of high- and low-luminosity FRBs at different frequencies. It is found that the event rates of these sub-samples of repeating FRBs similarly exceed the star formation rate at lower redshift than 1. Interestingly, we confirm with bootstrap method that the event rates of low-frequency FRBs exhibit different evolution patterns and are higher than that of high-frequency ones. △ Less

Submitted 15 September, 2025; originally announced September 2025.

Comments: 11 pages, 7 figures and 5 tables. Comments are welcome

Cross-correlations between the CLAMATO Lyman-alpha forest and galaxies within the COSMOS field

Authors: Benjamin Zhang, Khee-Gan Lee, Andrei Cuceu, Andreu Font-Ribera, Rieko Momose

Abstract: We compute the 3D cross-correlation between the absorption of the $z\sim 2.3$ Lyman-alpha forest measured by the COSMOS Lyman-Alpha Mapping And Tomography Observations (CLAMATO) survey, and 1642 foreground galaxies with spectroscopic redshifts from several different surveys, including 3D-HST, CLAMATO, zCOSMOS-Deep, MOSDEF, and VUDS. For each survey, we compare the measured cross-correlation with m… ▽ More We compute the 3D cross-correlation between the absorption of the $z\sim 2.3$ Lyman-alpha forest measured by the COSMOS Lyman-Alpha Mapping And Tomography Observations (CLAMATO) survey, and 1642 foreground galaxies with spectroscopic redshifts from several different surveys, including 3D-HST, CLAMATO, zCOSMOS-Deep, MOSDEF, and VUDS. For each survey, we compare the measured cross-correlation with models incorporating the galaxy linear bias as well as observed redshift dispersion and systematic redshift offset. The derived redshift dispersion and offsets are generally consistent with those expected from, e.g., spectroscopic redshifts measured with UV absorption lines or NIR emission lines observed with specific instruments, but we find hints of `fingers-of-god' caused by overdensities in the field. We combine our foreground galaxy sample, and split them into 3 bins of robustly-estimated stellar mass in order to study the stellar mass-halo mass relationship. For sub-samples with median stellar masses of $\log_{10}(M_* / M_\odot) = [9.23,9.71,10.21]$, we find galaxy biases of $b_g\approx [2.9, 3.3,4.7]$, respectively. A comparison with mock measurements from the Bolshoi-Planck $N$-body simulation yields corresponding halo masses of $\log_{10}(M_* / M_\odot) \approx [10.3,11.6,12.1]$ for these stellar mass bins. At the low mass end, our results suggest enhanced star formation histories in mild tension with predictions from previous angular correlation and abundance matching-based observations, and the IllustrisTNG simulation. △ Less

Submitted 9 September, 2025; originally announced September 2025.

Comments: 16 pages, 9 figures, 3 tables. Comments welcome

Parkes transient events: II. Pulsar single pulses database containing raw data segment

Authors: Xuan Yang, S. B. Zhang, Le-Yu Tang, L. Toomey, Xue-Feng Wu

Abstract: We have re-processed single pulse candidates from the first four years (1997-2001) of the Parkes Multibeam receiver system observations, creating a new Parkes transient database (PTD II) that contains 165,592 single pulses from 363 known pulsars. Unlike previous databases, PTD II preserves the critical raw data segments of each detected pulse, enabling detailed analyses of emission physics while m… ▽ More We have re-processed single pulse candidates from the first four years (1997-2001) of the Parkes Multibeam receiver system observations, creating a new Parkes transient database (PTD II) that contains 165,592 single pulses from 363 known pulsars. Unlike previous databases, PTD II preserves the critical raw data segments of each detected pulse, enabling detailed analyses of emission physics while maintaining a compact size of only 1.5 GB. The database employs a sqlite3 structure organising pulsar metadata, observation files, and pulse events with their raw data stored in binary format. We provide processing tools for extracting and analysing single-pulse data, enabling fluence fitting and statistical analysis. Our pulsars exhibit diverse fluence distributions, such as log-normal, Gaussian, and unimodal. Temporal analyses reveal significant evolution in emission characteristics of several pulsars, including event rate variations spanning two orders of magnitude in PSR J1602-5100 and PSR J0942-5552. Beyond supporting fundamental pulsar emission studies, the database serves as a valuable training resource for developing new single-pulse detection algorithms in the presence of radio frequency interference. △ Less

Submitted 19 August, 2025; originally announced August 2025.

Comments: 24 pages, 9 figures, Accepted for publication in ApJS

Multiwavelength Observations of the Apparently Non-repeating FRB 20250316A

Authors: Ye Li, Hui Sun, Lei Qian, Dong-Yue Li, Yan-Long Hua, Li-Ping Xin, Cheng-Kui Li, Yi-Han Wang, Jia-Rui Niu, Tian-Rui Sun, Zhu-Heng Yao, Jin-Jun Geng, Chi-Chuan Jin, Nanda Rea, Yuan Liu, Zhi-Chen Pan, Tao An, Vadim Burwitz, Zhi-Ming Cai, Jin-Huang Cao, Yong Chen, Hua-Qing Cheng, Wei-Wei Cui, Hua Feng, Peter Friedrich , et al. (50 additional authors not shown)

Abstract: The physical origin of fast radio bursts (FRBs) remains uncertain. Although multiwavelength observations have been widely conducted, only Galactic FRB~20200428D is associated with an X-ray burst from the magnetar SGR J1935+2154. Here, we present multiwavelength follow-up observations of the nearby bright FRB~20250316A, including the Five-hundred-meter Aperture Spherical radio Telescope (FAST), Ein… ▽ More The physical origin of fast radio bursts (FRBs) remains uncertain. Although multiwavelength observations have been widely conducted, only Galactic FRB~20200428D is associated with an X-ray burst from the magnetar SGR J1935+2154. Here, we present multiwavelength follow-up observations of the nearby bright FRB~20250316A, including the Five-hundred-meter Aperture Spherical radio Telescope (FAST), Einstein Probe (EP) X-ray mission, Chandra X-ray Observatory, Wide Field Survey Telescope (WFST) and Space Variable Object Monitor/Visible Telescope (SVOM/VT). The 13.08-hour FAST follow-up campaign without pulse detection requires an energy distribution flatter than those of well-known repeating FRBs, suggesting that this burst is likely a one-off event. A prompt EP follow-up and multi-epoch observational campaign totaling $>$ 100 ks led to the detection of an X-ray source within the angular resolution of its Follow-up X-ray Telescope (FXT, $10^{\prime\prime}$). A subsequent Chandra observation revealed this source to be offset by $7^{\prime\prime}$ from the FRB position, and established a 0.5-10 keV flux upper limit of $7.6\times 10^{-15}$ $\rm erg\,cm^{-2}\,s^{-1}$ at the FRB position, corresponding to $\sim 10^{39}$ $\rm erg\,s^{-1}$ at the 40 Mpc distance of the host galaxy NGC~4141. These results set one of the most stringent limits on X-ray emission from a non-repeating FRB, disfavoring ultra-luminous X-ray sources (ULXs) as counterparts of apparently one-off FRBs and offering critical insights into afterglow models. Our study suggests that an arcsecond localization of both the FRB and its potential X-ray counterpart is essential for exploring the X-ray counterpart of an FRB. △ Less

Submitted 18 November, 2025; v1 submitted 19 August, 2025; originally announced August 2025.

Comments: Accepted for publication in The Astrophysical Journal

Magnetars in Binaries as the Engine of Actively Repeating Fast Radio Bursts

Authors: Bing Zhang, Rui-Chong Hu

Abstract: The association between FRB 20200428D and the Galactic magnetar SGR J1935+2154 makes magnetars the leading engine of cosmological fast radio bursts (FRBs). However, there is a list of puzzles for this magnetar-for-all-FRBs scenario: known Galactic magnetars are all isolated and none of them are active repeaters; some cosmological repeaters have extremely high repetition rates but without any measu… ▽ More The association between FRB 20200428D and the Galactic magnetar SGR J1935+2154 makes magnetars the leading engine of cosmological fast radio bursts (FRBs). However, there is a list of puzzles for this magnetar-for-all-FRBs scenario: known Galactic magnetars are all isolated and none of them are active repeaters; some cosmological repeaters have extremely high repetition rates but without any measurable spin-related periodicity; some show long-term periodic active windows; and some show diverse rotation measure (RM) evolution patterns, such as quasi-periodic fluctuations, sign reversals, and abrupt RM flares. Here we propose a unified theoretical framework for FRBs within the framework of magnetar engine: Most active repeating FRBs originate from magnetars in binary systems with nearly aligned rotation and magnetic axes, some of which with a triple-aligned geometry, i.e. with an alignment with the orbital axis as well; whereas apparent non-repeaters and inactive repeaters originate from magnetars in isolated systems or in binaries with a misaligned geometry. By studying various magnetar formation channels using population syntheses, we show that a few percent of magnetars in the universe can be in binary systems, most with a massive star companion and some with aligned geometry. We suggest that such binary systems can account for the rich phenomenology of active repeaters. We suggest that the existence of a companion helps to maintain the aligned geometry and that the companion may play an active role in triggering FRBs in an active repeater source. △ Less

Submitted 8 October, 2025; v1 submitted 16 August, 2025; originally announced August 2025.

Comments: 20 pages, 5 figures, version accepted for publication in ApJL

Dark Matter and the Early Formation of Supermassive Black Holes

Authors: Andrew Imai, Grant J. Mathews, Guobao Tang, Brian Zhang

Abstract: We investigate the growth of supermassive black holes (SMBHs) at high redshift ($z \ge 10$) from a combination of dark matter capture, black-hole mergers, and gas accretion. It has previously been shown that SMBHs can form by $z \approx 10$ via black-hole mergers, Eddington-limited Bondi gas accretion and tidal disruption events with stars within dense nuclear clusters. Here, we show that the capt… ▽ More We investigate the growth of supermassive black holes (SMBHs) at high redshift ($z \ge 10$) from a combination of dark matter capture, black-hole mergers, and gas accretion. It has previously been shown that SMBHs can form by $z \approx 10$ via black-hole mergers, Eddington-limited Bondi gas accretion and tidal disruption events with stars within dense nuclear clusters. Here, we show that the capture of collisionless dark matter by a growing SMBH also substantially contributes, in some cases by an order of magnitude to the final SMBH mass. In particular, we show that a small seed stellar-remnant black hole can more easily reach $> 10^7$ M$_{\odot}$ by $z = 10$ in the core of dense nuclear star clusters when dark matter is included. This remains true for either cold dark matter or ultralight dark matter if the mass of the ULDM particle is $^>_\sim 10^{-20}$ eV. We highlight the unique evolution of ULDM capture by the growing SMBH when the ULDM de Broglie wavelength exceeds the initial nuclear star cluster half-mass radius. △ Less

Submitted 15 August, 2025; originally announced August 2025.

Tracing the Physical Lineage of GRB 211211A: Population Constraints on NS-WD Merger Gamma-Ray Bursts

Authors: Xiao-Tian Xu, Bin-Bin Zhang, Yun-Lang Guo, Xiang-Dong Li

Abstract: The peculiar long gamma-ray burst (GRB) event, GRB 211211A, is known for it is association with a kilonova feature. Whereas most long GRBs are thought to originate in the core collapse of massive stars, the presence of kilonova suggests GRB 211211A was instead produced by a merger of a compact object binary. Building on the interpretation put forward by \citet{Yang2022Natur.612..232Y}--who argue t… ▽ More The peculiar long gamma-ray burst (GRB) event, GRB 211211A, is known for it is association with a kilonova feature. Whereas most long GRBs are thought to originate in the core collapse of massive stars, the presence of kilonova suggests GRB 211211A was instead produced by a merger of a compact object binary. Building on the interpretation put forward by \citet{Yang2022Natur.612..232Y}--who argue that GRB 211211A was powered by a massive white-dwarf + neutron-star (WD-NS) merger--we adopt this WD-NS scenario as our observationally supported starting point. If the burst truly originates from that channel, its rarity must mirror the formation and merger rate of WD-NS binaries--a rate still largely unexplored in conventional massive-binary population studies. In this letter, we present a qualitative analysis based on binary evolution physics in order to understand the fraction of GRB 211211A in short GRBs (NS-WD/NS-NS fraction). Since the progenitors of massive WD-NS binaries occupy the initial mass function-preferred regime, where the zero-age main-sequence mass range of the assumed WD mass range (1.2-1.4$\,M_\odot$) is comparable to that of NSs, the NS-WD/NS-NS fraction emerging from our standard evolutionary path is expected to be $\sim$14--37\%, far higher than the observed fraction ($\sim5$\%). This discrepancy might imply a large, still-unidentified population of GRB 211211A-like events or an unusual origin of the NS-such as being hypernova-born or accretion-induced-collapse-born. Placing these results in a broader compact-binary context, implications for black-hole systems are also discussed. △ Less

Submitted 31 October, 2025; v1 submitted 14 August, 2025; originally announced August 2025.

Comments: accepted by ApJ after adding more details and discussion according to the referee's feedback

Neutrino and Electromagnetic Signals from Tidal Disruption Events: Bridging the Theory with Observations

Authors: Chengchao Yuan, Walter Winter, Cecilia Lunardini, B. Theodore Zhang, Kohta Murase, Bing Zhang

Abstract: This proceeding presents recent results from a joint analysis of time-dependent neutrino and electromagnetic emissions from tidal disruption events (TDEs), using both isotropic wind models and relativistic jets. We discuss constraints from Fermi Large Area Telescope (LAT) $γ$-ray upper limits on the size of the radiation zone and the maximum energies of accelerated cosmic rays, as well as the resu… ▽ More This proceeding presents recent results from a joint analysis of time-dependent neutrino and electromagnetic emissions from tidal disruption events (TDEs), using both isotropic wind models and relativistic jets. We discuss constraints from Fermi Large Area Telescope (LAT) $γ$-ray upper limits on the size of the radiation zone and the maximum energies of accelerated cosmic rays, as well as the resulting neutrino productions from TDEs and candidates, including AT 2019dsg, AT 2019fdr, AT 2019aalc, and AT 2021lwx. The Fermi upper limits correspond to a generic neutrino detection rate of $\lesssim0.01-0.1$ per TDE. Additionally, we explore multi-wavelength modeling of jetted TDEs with luminous X-ray afterglows, another TDE subclass, by incorporating the dynamics of structured jets with time-dependent energy injection. We also examine the connection between neutrinos and their multi-wavelength counterparts, highlighting implications for future multi-messenger discoveries with IceCube, IceCube-Gen2, KM3NeT, and Fermi-LAT. △ Less

Submitted 11 August, 2025; originally announced August 2025.

Comments: Presented at the 39th International Cosmic Ray Conference (ICRC 2025), 8 pages, 4 figures

Radio continuum and \HI 21-cm line observations of a nearby luminous infrared galaxy IRAS 17526+3253

Authors: Jianfeng Wu, Zhongzu Wu, Yulia Sotnikova, Bo Zhang, Yongjun Chen, Timur Mufakharov, Zhiqiang Shen

Abstract: We present results from our EVN and GMRT observations of the radio continuum and spectral line emission in IRAS 17526+3253, along with an analysis of its arcsecond-scale radio properties using archival VLA data. The EVN observations detected radio continuum emission from both the northwest (NW) and southeast (SE) nuclei. The NW nucleus shows two components with high brightness temperatures and rad… ▽ More We present results from our EVN and GMRT observations of the radio continuum and spectral line emission in IRAS 17526+3253, along with an analysis of its arcsecond-scale radio properties using archival VLA data. The EVN observations detected radio continuum emission from both the northwest (NW) and southeast (SE) nuclei. The NW nucleus shows two components with high brightness temperatures and radio luminosities, likely indicating the presence of an AGN core and jet. Meanwhile, our EVN observation failed to detect the OH line emission, possibly due to radio frequency interference and/or the emission being partly resolved out and below our detection limit. The multi-band radio spectral energy distribution (SED) deviates from a single power-law at low frequencies, suggesting low-frequency absorption. The GMRT spectral line data reveal both \HI absorption and emission. The \HI emission is diffuse and shows a velocity gradient from about 7500 \kms in the NW to 7800 \kms in the SE nucleus. On larger scales, the \HI emission extends about 4' along the NW-SE direction, with the southeastern extension matching the optical tidal tail. In addition, the weak \HI absorption features show broad line profiles, possibly due to overlapping \HI gas from the two nuclei. The aforementioned results are consistent with properties of intermediate-stage mergers reported in the literature. △ Less

Submitted 8 August, 2025; originally announced August 2025.

Comments: 23 pages, 18 figures, accepted by A&A Journal

Hubble constant constraint using 117 FRBs with a more accurate probability density function for ${\rm DM}_{\rm diff}$

Authors: Jiaming Zhuge, Marios Kalomenopoulos, Bing Zhang

Abstract: Fast radio bursts (FRBs) are among the most mysterious astronomical transients. Due to their short durations and cosmological distances, their dispersion measure (DM) - redshift ($z$) relation is useful for constraining cosmological parameters and detecting the baryons in the Universe. The increasing number of localized FRBs in recent years has provided more precise constraints on these parameters… ▽ More Fast radio bursts (FRBs) are among the most mysterious astronomical transients. Due to their short durations and cosmological distances, their dispersion measure (DM) - redshift ($z$) relation is useful for constraining cosmological parameters and detecting the baryons in the Universe. The increasing number of localized FRBs in recent years has provided more precise constraints on these parameters. However, the larger dataset reveals limitations in the widely used probability density function ($p_{\rm diff}$) for ${\rm DM}_{\rm diff}$, which refers to the diffuse electron term of FRB DM. In this project, we collect 117 of the latest, localized FRBs, discuss the effect of a more accurate $σ_{\rm diff}$, which is a parameter in $p_{\rm diff}$ and once thoughts as ``effective standard deviation'', and more clearly rewrite their likelihood to better constrain the parameters above. We find that the widely used approximation $σ_{\rm diff} \sim F/\sqrt{z}$ only works under contrived assumptions and shows the greatest deviation from the true standard deviation in low redshift. In general, one should use an accurate method to derive this parameter from $p_{\rm diff}$. Our method yields better constraints on $H_0Ω_b f_{\rm diff} = 2.813_{-0.258}^{+0.250}\;{\rm km/s/Mpc}$ or $H_0 = 66.889_{-5.459}^{+6.754} \;{\rm km/s/Mpc}$ when combining the FRB data with CMB measurements and taking $f_{\rm diff} = 0.84$. This fully analytical correction helps us better constrain cosmological parameters with the increasing number of localized FRBs available today. △ Less

Submitted 6 November, 2025; v1 submitted 7 August, 2025; originally announced August 2025.

Comments: Accepted for publication in ApJ

The Size Evolution and the Size-Mass Relation of Lyman-Alpha Emitters across $3 \lesssim z < 7$ as Observed by JWST

Authors: Qi Song, F. S. Liu, Jian Ren, Pinsong Zhao, Qifan Cui, Yubin Li, Hao Mo, Yuchong Luo, Guanghuan Wang, Nan Li, Hassen M. Yesuf, Weichen Wang, Xin Zhang, Xianmin Meng, Mingxiang Fu, Bingqing Zhang, Chenxiaoji Ling

Abstract: Understanding the morphological structures of Lyman-alpha emitters (LAEs) is crucial for unveiling their formation pathways and the physical origins of Ly$α$ emission. However, the evolution of their sizes and structural scaling relations remains debated. In this study, we analyze a large sample of 876 spectroscopically confirmed LAEs at $3 \lesssim z < 7$, selected from the MUSE, VANDELS, and CAN… ▽ More Understanding the morphological structures of Lyman-alpha emitters (LAEs) is crucial for unveiling their formation pathways and the physical origins of Ly$α$ emission. However, the evolution of their sizes and structural scaling relations remains debated. In this study, we analyze a large sample of 876 spectroscopically confirmed LAEs at $3 \lesssim z < 7$, selected from the MUSE, VANDELS, and CANDELSz7 surveys in the GOODS-S, UDS, and COSMOS fields. Utilizing James Webb Space Telescope (JWST) NIRCam imaging data, we measure their rest-frame UV and optical V-band effective radii ($R_{\rm e}$) through two-dimensional Sérsic profile fitting. Our results show that these LAEs are generally compact, with a median $R_{\rm e,UV}$ of 0.50$^{+0.30}_{-0.24}$ kpc and a median $R_{\rm e,V}$ of 0.57$^{+0.33}_{-0.24}$ kpc. The size evolution follows $R_{\rm e,UV} \propto (1 + z)^{-0.91 \pm 0.10}$ and $R_{\rm e,V} \propto (1 + z)^{-0.93 \pm 0.18}$, respectively. Their UV and optical sizes are statistically comparable, indicating negligible UV-to-optical color gradients. For the first time, we establish the rest-frame optical size-mass relation for LAEs at $z>3$, finding slopes comparable to typical star-forming galaxies (SFGs), but with slightly smaller sizes at a given stellar mass. These results provide important clues for understanding structural evolution of LAEs in the early universe. △ Less

Submitted 9 November, 2025; v1 submitted 7 August, 2025; originally announced August 2025.

Comments: 16 pages, 11 figures, 3 tables. Accepted for publication in ApJ

Spectral Energy Correlations of Gamma-Ray Bursts from Structured Jets

Authors: X. L. Zhang, Z. B. Zhang, Y. F. Huang, D. Li, X. J. Li, L. M. Song

Abstract: Using 148 out-axis gamma-ray bursts, we build their spectrum-energy relations of peak energy versus isotropic energy, peak energy versus peak luminosity and peak energy versus jet-calibrated energy which are corrected for a structured jet model. These relations are found to depend on the observer's viewing angle as long as the observer is within the jet cone. After converting the out-axis energy r… ▽ More Using 148 out-axis gamma-ray bursts, we build their spectrum-energy relations of peak energy versus isotropic energy, peak energy versus peak luminosity and peak energy versus jet-calibrated energy which are corrected for a structured jet model. These relations are found to depend on the observer's viewing angle as long as the observer is within the jet cone. After converting the out-axis energy relations to the in-axis situations, we find that the corresponding in-axis energy relations are universally steeper, of which all of them can be roughly interpreted by the Synchrotron radiation mechanism as shown in Xu et al.. Meanwhile, we notice that the in-axis means of isotropic energies are about one order of magnitude larger than the out-axis means for both short and long bursts except the Supernova-associated gamma-ray bursts. Furthermore, we apply all the newly-found energy relations to construct the Hubble diagrams of out/in-axis bursts. It is found that the in-axis Hubble diagrams are better cosmological indicators. △ Less

Submitted 6 August, 2025; originally announced August 2025.

Comments: 29 pages, 12 figures and 3 tables, accepted by ApJ

A 50 s quasi-periodic oscillation in the early X-ray afterglow of GRB 220711B

Authors: H. Gao, W. -H. Lei, S. Xiao, Z. -P. Zhu, L. Lan, S. -K. Ai, A. Li, N. Xu, T. -C. Wang, B. Zhang, D. Xu, J. P. U. Fynbo, K. E. Heintz, P. Jakobsson, D. A. Kann, S. -Y. Fu, S. -Q. Jiang, X. Liu, S. -L. Xiong, W. -X. Peng, X. -B. Li, W. -C. Xue

Abstract: It is generally believed that long duration gamma-ray bursts (GRBs) originate from the core collapse of rapidly spinning massive stars and at least some of them are powered by hyper-accreting black holes. However, definite proofs about the progenitor and central engine of these GRBs have not been directly observed in the past. Here we report the existence of a Quasi-Periodic Oscillation (QPO) sign… ▽ More It is generally believed that long duration gamma-ray bursts (GRBs) originate from the core collapse of rapidly spinning massive stars and at least some of them are powered by hyper-accreting black holes. However, definite proofs about the progenitor and central engine of these GRBs have not been directly observed in the past. Here we report the existence of a Quasi-Periodic Oscillation (QPO) signature with periodic frequency $\sim$0.02 Hz in the early X-ray afterglow phase of GRB 220711B. Such a low-frequency QPO likely signals the precession of a relativistic jet launched from a GRB hyper-accreting black hole central engine. The energy injection signature from the \textbf{late} X-ray observations (from $5\times 10^2s\sim 1\times10^4s$) is consistent with the precession hypothesis. The prompt $γ$-ray light curve does not show any QPO signature, suggesting that the X-ray flaring emission in the early afterglow phase and prompt emission likely originate from different accretion processess, indicating that the progenitor stars of GRBs have a core-envelope structure with a stratified angular momentum distribution and the late-time accretion disk likely has a misalignment with respect to the rotation axis of the black hole. Such a misalignment is not expected in a canonical collapsar model. As a result, the QPO signature in GRB 220711B may reveal a new formation channel of long GRBs, possibly a stellar-merger-induced core collapse, with the orbital angular momentum of the binary misaligned with the spin axis of the collapsing star. △ Less

Submitted 31 July, 2025; originally announced August 2025.

Comments: 21 pages, 8 figures, published in APJ, 2025ApJ...985...33G

SVOM GRB 250314A at z $\simeq$ 7.3: an exploding star in the era of reionization

Authors: B. Cordier, J. Y. Wei, N. R. Tanvir, S. D. Vergani, D. B. Malesani, J. P. U. Fynbo, A. de Ugarte Postigo, A. Saccardi, F. Daigne, J. -L. Atteia, O. Godet, D. Gotz, Y. L. Qiu, S. Schanne, L. P. Xin, B. Zhang, S. N. Zhang, A. J. Nayana, L. Piro, B. Schneider, A. J. Levan, A. L. Thakur, Z. P. Zhu, G. Corcoran, N. A. Rakotondrainibe , et al. (81 additional authors not shown)

Abstract: Most long Gamma-ray bursts originate from a rare type of massive stellar explosion. Their afterglows, while rapidly fading, can be initially extremely luminous at optical/near-infrared wavelengths, making them detectable at large cosmological distances. Here we report the detection and observations of GRB 250314A by the SVOM satellite and the subsequent follow-up campaign with the near-infrared af… ▽ More Most long Gamma-ray bursts originate from a rare type of massive stellar explosion. Their afterglows, while rapidly fading, can be initially extremely luminous at optical/near-infrared wavelengths, making them detectable at large cosmological distances. Here we report the detection and observations of GRB 250314A by the SVOM satellite and the subsequent follow-up campaign with the near-infrared afterglow discovery and the spectroscopic measurements of its redshift z $\simeq$ 7.3 . This burst happened when the Universe was only $\sim$ 5% of its current age. We discuss the signature of these rare events within the context of the SVOM operating model, and the ways to optimize their identification with adapted ground follow-up observation strategies. △ Less

Submitted 24 July, 2025; originally announced July 2025.

Comments: 12 pages, 11 Figures, 5 Tables, submitted to A&AL

EP250108a/SN2025kg: A Magnetar-powered Gamma-Ray Burst Supernova Originating from a Close Helium-star Binary via Isolated Binary Evolution

Authors: Jin-Ping Zhu, Jian-He Zheng, Bing Zhang

Abstract: SN\,2025kg, linked to EP250108a, is among the brightest broad-lined Type Ic supernova (SN Ic-BL) known, showing unique helium absorptions, a late-time broad H$α$, and an early bump. In this {\em{Letter}}, we propose a jet-cocoon origin to explain EP250108a as off-axis cooling emission from a mildly relativistic inner cocoon viewed at $\sim45^\circ$ and the early bump of SN\,2025kg as the outer coc… ▽ More SN\,2025kg, linked to EP250108a, is among the brightest broad-lined Type Ic supernova (SN Ic-BL) known, showing unique helium absorptions, a late-time broad H$α$, and an early bump. In this {\em{Letter}}, we propose a jet-cocoon origin to explain EP250108a as off-axis cooling emission from a mildly relativistic inner cocoon viewed at $\sim45^\circ$ and the early bump of SN\,2025kg as the outer cocoon cooling emission, both constraining an energy of $\sim(1-2)\times10^{52}{\rm{erg}}$ and a progenitor radius of $\sim5\,R_\odot$. To explain SN\,2025kg's exceptionally luminous peak, potential energy injection into the $\sim2.5\,M_\odot$ ejecta from a magnetar with initial period $\sim1.7\,{\rm{ms}}$ and magnetic field $\sim2\times10^{15}{\rm{G}}$ may be required, implying a rapidly rotating $\sim4\,M_\odot$ progenitor. Thus, the progenitor may be a low-mass helium star with an extended helium envelope, supported by helium absorption lines and an inferred weak pre-SN wind. Hydrogen-rich material may reside in the inner ejecta layers, as suggested by the late-time broad H$α$, possibly originating from main-sequence companion material evaporated by the magnetar wind. Since the observed near-solar metallicity challenges the popular quasi-chemically homogeneous evolution channel, the rapidly rotating helium-star progenitor of EP250108a/SN\,2025kg might attain angular momentum by being tidally spun up by a main-sequence companion in a close binary formed through isolated binary evolution. △ Less

Submitted 5 November, 2025; v1 submitted 24 July, 2025; originally announced July 2025.

Comments: 11 pages, 5 figures, accepted by MNRAS Letters

Decadal evolution of a repeating fast radio burst source

Authors: P. Wang, J. S. Zhang, Y. P. Yang, D. K. Zhou, Y. K. Zhang, Y. Feng, Z. Y. Zhao, J. H. Fang, D. Li, W. W. Zhu, B. Zhang, F. Y. Wang, Y. F. Huang, R. Luo, J. L. Han, K. J. Lee, C. W. Tsai, Z. G. Dai, H. Gao, X. P. Zheng, J. H. Cao, X. L. Chen, E. Gugercinoglu, J. C. Jiang, W. C. Jing , et al. (26 additional authors not shown)

Abstract: The origin of fast radio bursts (FRBs), the brightest cosmic radio explosions, is still unknown. Bearing critical clues to FRBs' origin, the long-term evolution of FRBs has yet to be confirmed, since the field is still young and most FRBs were seen only once. Here we report clear evidence of decadal evolution of FRB~20121102A, the first precisely localized repeater. In conjunction with archival da… ▽ More The origin of fast radio bursts (FRBs), the brightest cosmic radio explosions, is still unknown. Bearing critical clues to FRBs' origin, the long-term evolution of FRBs has yet to be confirmed, since the field is still young and most FRBs were seen only once. Here we report clear evidence of decadal evolution of FRB~20121102A, the first precisely localized repeater. In conjunction with archival data, our FAST and GBT monitoring campaign since 2020 reveals a significant 7% decline of local dispersion measure (DM). The rotation measure (RM) of 30,755$\pm$16 $\mathrm{rad\,m^{-2}}$ detected in the last epoch represents a 70% decrease compared to that from December 2016. The $σ_{RM}$ parameter, which describes the complexity of the magneto-ionic environment surrounding the source, was shown to have decreased by 13%. These general trends reveal an evolving FRB environment, which could originate from an early-phase supernova associated with an enhanced pair wind from the FRB central engine. △ Less

Submitted 21 July, 2025; originally announced July 2025.

Comments: 85 pages, 14 figures, under review of Nature Astronomy

Investigating FRB 20240114A with FAST: Morphological Classification and Drifting Rate Measurements in a Burst-Cluster Framework

Authors: Long-Xuan Zhang, Shiyan Tian, Junyi Shen, Jun-Shuo Zhang, Dejiang Zhou, Lin Zhou, Po Ma, Tian-Cong Wang, Dengke Zhou, Jinlin Han, Yunpeng Men, Fayin Wang, Jiarui Niu, Pei Wang, Weiwei Zhu, Bing Zhang, Di Li, Yuan-Chuan Zou, Wei-Yang Wang, Yuan-Pei Yang, Qin Wu, He Gao, Ke-Jia Lee, Jia-Wei Luo, Rui Luo , et al. (43 additional authors not shown)

Abstract: This study investigates the morphological classification and drifting rate measurement of the repeating fast radio burst (FRB) source FRB20240114A using the Five-hundred-meter Aperture Spherical Telescope (FAST). Detected on January 14, 2024, FRB20240114A showed an exceptionally high burst rate. During a continuous 15,780-second monitoring session on March 12, 2024, 3,203 bursts (2,109 burst-clust… ▽ More This study investigates the morphological classification and drifting rate measurement of the repeating fast radio burst (FRB) source FRB20240114A using the Five-hundred-meter Aperture Spherical Telescope (FAST). Detected on January 14, 2024, FRB20240114A showed an exceptionally high burst rate. During a continuous 15,780-second monitoring session on March 12, 2024, 3,203 bursts (2,109 burst-clusters) were detected. We refine the definitions of sub-bursts, bursts, and burst-clusters. Using an average dispersion measure (DM) of 529.2 pc cm$^{-3}$, burst-clusters were classified into Downward Drifting, Upward Drifting, No Drifting, No Evidence for Drifting, Not-Clear, and Complex categories. Notably, 233 (23.82%) of the 978 drifting burst-clusters showed upward drifting. Excluding 142 upward drifting single-component clusters, the remaining 91 upward drifting double- or multiple-components clusters account for 10.89% of the drifting sample. Further restricting to those with consecutive time intervals, only 9 upward drifting bursts remain. An inverse correlation is found between drifting rate and sub-burst effective width. Upward drifting single-component clusters tend to have smaller effective widths, bandwidths, and fluxes than downward drifting ones. For these upward drifting clusters, drifting rate increases with peak frequency. A Kolmogorov-Smirnov test reveals longer consecutive intervals in upward drifting clusters compared to downward ones, suggesting differing underlying mechanisms. △ Less

Submitted 19 July, 2025; originally announced July 2025.

Comments: 22 pages, 13 figures, 1 tables, the 3rd of papers from the FAST FRB Key Science Project Collaboration on FRB 20240114A: Burst Morphology Analysis

A comprehensive search for Long and Short Periodic Features from an Extremely Active Cycle of FRB 20240114A

Authors: Dengke Zhou, Pei Wang, Jianhua Fang, Weiwei Zhu, Bing Zhang, Di Li, Yi Feng, Yong-Feng Huang, Ke-Jia Lee, Jinlin Han, Yuan-Chuan Zou, Jun-Shuo Zhang, Shuo Xiao, Rui Luo, Long-Xuan Zhang, Tian-Cong Wang, Wanjin Lu, Jinhuang Cao, Wenfei Yu, Bing Li, Chen-Chen Miao, Jintao Xie, Yunchuan Chen, Han Wang, Yuanhong Qu , et al. (34 additional authors not shown)

Abstract: Possible periodic features in fast radio bursts (FRBs) may provide insights into their astrophysical origins. Using extensive observations from the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we conduct a multi-timescale periodicity search for the exceptionally active repeater FRB~20240114A. Our analysis is based on different datasets for different timescales: for short-timescale… ▽ More Possible periodic features in fast radio bursts (FRBs) may provide insights into their astrophysical origins. Using extensive observations from the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we conduct a multi-timescale periodicity search for the exceptionally active repeater FRB~20240114A. Our analysis is based on different datasets for different timescales: for short-timescale periodicity in Time of Arrivals (TOAs), we use 57 observations from January to August 2024; for long-timescale periodicity, we employ an extended TOA dataset comprising 111 observations spanning from January 2024 to October 2025; and for burst time series analysis, we utilize individual burst data from the 57 FAST observations. We identify three candidate short-timescale periodic signals (0.673~s, 0.635~s, and 0.536~s) with significances of $3.2σ$--$6σ$, each detected in two independent observations. On longer timescales, we detect a significant $143.40\pm7.19$-day periodicity with $5.2σ$ significance, establishing FRB~20240114A as a periodic repeater. In burst time series, we find quasi-periodic oscillations in the few hundred Hz range ($3.4σ$ and $3.7σ$) and periodic burst trains with periods of several to tens of milliseconds ($3σ$--$3.9σ$), though these periodic features appear transient and short-lived. The detection of periodic signals at these different time scales indicates that FRB 20240114A exhibits intriguing periodic self-similar characteristics. Despite the comprehensive dataset, no definitive periodicity linked to the source's rotation is confirmed, placing stringent constraints on the intrinsic source properties and the modulation mechanisms. All data are available via the Science Data Bank. △ Less

Submitted 7 November, 2025; v1 submitted 19 July, 2025; originally announced July 2025.

Comments: The 2nd of papers from the FAST FRB Key Science Project Collaboration on FRB 20240114A: (quasi-) period search

The magnetar model's energy crisis for a prolific repeating fast radio burst source

Authors: Jun-Shuo Zhang, Tian-Cong Wang, Pei Wang, Qin Wu, Di Li, Weiwei Zhu, Bing Zhang, He Gao, Ke-Jia Lee, Jinlin Han, Chao-Wei Tsai, Fayin Wang, Yong-Feng Huang, Yuan-Chuan Zou, Dengke Zhou, Wanjin Lu, Jintao Xie, Jianhua Fang, Jinhuang Cao, Chen-Chen Miao, Yuhao Zhu, Yunchuan Chen, Xiaofeng Cheng, Yinan Ke, Yong-Kun Zhang , et al. (39 additional authors not shown)

Abstract: Fast radio bursts (FRBs) are widely considered to originate from magnetars that power the explosion through releasing magnetic energy. Active repeating FRBs have been seen to produce hundreds of bursts per hour and can stay active for months, thus may provide stringent constraints on the energy budget of FRBs' central engine. Within a time span of 214 days, we detected 11,553 bursts from the hyper… ▽ More Fast radio bursts (FRBs) are widely considered to originate from magnetars that power the explosion through releasing magnetic energy. Active repeating FRBs have been seen to produce hundreds of bursts per hour and can stay active for months, thus may provide stringent constraints on the energy budget of FRBs' central engine. Within a time span of 214 days, we detected 11,553 bursts from the hyper-active FRB 20240114A that reached a peak burst rate of 729 hr$^{-1}$. This is the largest burst sample from any single FRB source, exceeding the cumulative total of all published bursts from all known FRBs to date. Assuming typical values of radio efficiency and beaming factor, the estimated total isotropic burst energy of this source exceeds 86% of the dipolar magnetic energy of a typical magnetar. The total released energy from this source exceeds that of other known repeaters by about one and a half orders of magnitude, yielding the most stringent lower limit of $4.7\times10^{32}$ G cm$^3$ for the magnetar's magnetic moment. The source remained active at the end of this observation campaign. Our findings thus require either the FRB's central magnetar engine's possessing exceptionally high emission efficiency or a more powerful compact object than a typical magnetar. △ Less

Submitted 30 August, 2025; v1 submitted 19 July, 2025; originally announced July 2025.

Comments: 33 pages, 6 figures, the 1st of papers from the FAST FRB Key Science Project Collaboration on FRB 20240114A: Energy Budget Analysis, under review of Nature Astronomy

Einstein Probe Discovery of EP J182730.0-095633: A New Black Hole X-ray Binary Candidate in Faint Outburst?

Authors: Huaqing Cheng, Qingchang Zhao, L. Tao, H. Feng, F. Coti Zelati, H. W. Pan, A. L. Wang, Y. N. Wang, M. Y. Ge, A. Rau, A. Marino, L. Zhang, W. J. Zhang, F. Carotenuto, L. Ji, C. C. Jin, D. Y. Li, B. F. Liu, Y. Liu, E. L. Qiao, N. Rea, R. Soria, S. Wang, Z. Yan, W. Yuan , et al. (56 additional authors not shown)

Abstract: Black hole X-ray binaries (candidates) currently identified in our galaxy are mainly transient sources, with the majority discovered through the detection of their X-ray outbursts. Among these, only four were found during faint outbursts exhibiting peak X-ray luminosities $L_{\rm X}\lesssim10^{36}~{\rm erg~s^{-1}}$, likely due to the previous lack of sensitive, wide-field monitoring instruments in… ▽ More Black hole X-ray binaries (candidates) currently identified in our galaxy are mainly transient sources, with the majority discovered through the detection of their X-ray outbursts. Among these, only four were found during faint outbursts exhibiting peak X-ray luminosities $L_{\rm X}\lesssim10^{36}~{\rm erg~s^{-1}}$, likely due to the previous lack of sensitive, wide-field monitoring instruments in the X-ray band. In this Letter, we present the discovery of an intriguing X-ray transient, EP J182730.0-095633, via the Einstein Probe (EP) and subsequent multi-wavelength follow-up studies. This transient, located on the Galactic plane, experienced a faint and brief X-ray outburst lasting about 20 days. Its X-ray spectrum is non-thermal and consistent with a power-law model with a nearly constant photon index of $Γ\sim2$ throughout the outburst. A long-lasting millihertz quasi-periodic oscillation (QPO) signal was detected in its X-ray light curve, centered around a frequency of $\sim0.04$ Hz. A transient near-infrared source was identified as its counterpart, although no optical emission was detectable, likely due to significant extinction. A radio counterpart was also observed, displaying an inverted radio spectrum with $α\sim0.45$. The X-ray spectral and temporal characteristics, along with the multi-wavelength properties, indicate that the source is a faint low-mass X-ray binary, with the compact object likely being a black hole. This work demonstrates the potential of the EP in discovering new X-ray binaries by capturing faint-level X-ray outbursts. △ Less

Submitted 17 July, 2025; originally announced July 2025.

Comments: 22 pages, 5 figures (plus 3 in appendix), 3 tables in appendix. Accepted for publication in ApJ Letters

VegasAfterglow: A High-Performance Framework for Gamma-Ray Burst Afterglows

Authors: Yihan Wang, Connery Chen, Bing Zhang

Abstract: Gamma-ray bursts (GRBs) are the most luminous astrophysical transients, known to be associated with core collapse of massive stars or mergers of two compact objects such as two neutron stars. They are followed by multi-wavelength afterglow emission originating from the deceleration of the relativistic jets by the ambient medium. The study of afterglow emission offers crucial insights into the phys… ▽ More Gamma-ray bursts (GRBs) are the most luminous astrophysical transients, known to be associated with core collapse of massive stars or mergers of two compact objects such as two neutron stars. They are followed by multi-wavelength afterglow emission originating from the deceleration of the relativistic jets by the ambient medium. The study of afterglow emission offers crucial insights into the physics of relativistic shocks, the properties of the circumburst environment, the physical and geometrical structure of relativistic jets, as well as the viewing geometry of the observer. We present {\tt VegasAfterglow}, a newly developed, high-performance C++ framework designed for modeling GRB afterglows with flexibility and computational efficiency as key features of design. The framework self-consistently solves forward and reverse shock dynamics and calculates synchrotron (including self-absorption or all spectral regimes) and inverse Compton radiation (including Klein-Nishina corrections); it can handle arbitrary user-defined ambient density profiles, central engine activity histories, viewing angles, and the jet structures of energy, Lorentz factor, and magnetization profiles. It supports both relativistic and non-relativistic regimes and includes lateral jet spreading effects. In this paper, we describe the numerical implementation of the framework and assess its computational performance. Our results demonstrate that {\tt VegasAfterglow} is well-suited for interpreting current and future multi-wavelength observations in the era of multi-messenger astronomy. △ Less

Submitted 30 September, 2025; v1 submitted 14 July, 2025; originally announced July 2025.

Comments: Accepted for publication in JHEAp. Comments are welcome. Code available at https://github.com/YihanWangAstro/VegasAfterglow

Einstein Probe discovery of the short period intermediate polar EP J115415.8-501810

Authors: Y. Xiao, M. Ge, N. Rea, F. Lu, H. Feng, L. Tao, D. de Martino, F. Coti Zelati, A. Marino, E. Kuulkers, W. Yuan, C. Jin, H. Sun, J. Wu, N. Hurley-Walker, S. J. McSweeney, D. A. H. Buckley, B. Zhang, S. Zhang, S. Scaringi, K. Mori, Z. Yu, X. Hou, Y. Xu

Abstract: The X-ray transient source EP240309a/EP\,J115415.8$-$501810 was first detected by the Wide-Field X-ray Telescope (WXT) on board Einstein Probe (EP) during the commissioning phase. Subsequent optical observations confirmed it as a Cataclysmic Variable of the intermediate polar type with a 238.2\,s spinning white dwarf in a $\sim$3.76\,hr orbit. We report on the source discovery and follow-up studie… ▽ More The X-ray transient source EP240309a/EP\,J115415.8$-$501810 was first detected by the Wide-Field X-ray Telescope (WXT) on board Einstein Probe (EP) during the commissioning phase. Subsequent optical observations confirmed it as a Cataclysmic Variable of the intermediate polar type with a 238.2\,s spinning white dwarf in a $\sim$3.76\,hr orbit. We report on the source discovery and follow-up studies made with the Follow-up X-ray Telescope (FXT) of EP. A periodic variation of 231\,s is detected in the 0.3$-$2\,keV band, while no obvious pulsation appears in the 2$-$10\,keV band. The spectral analysis shows that the X-ray emission could be described by an absorbed bremsstrahlung model with $kT$\textgreater\,11\,keV. The partial covering absorption, with an hydrogen column density $N_H$ = 2.0$\times 10^{22}\,\rm cm^{-2}$ and covering fraction around 0.9, is much larger than the interstellar absorption along the line of sight. According to the distance $d = 309.5$\,pc obtained from Gaia parallax, we estimate that the luminosity of this source in the 0.3$-$10\,keV range is $\sim 2\times10^{32}$\,erg\,s$^{-1}$. In addition, phase-resolved spectral analysis reveals that the detected periodic variation is mainly caused by the change in the absorption column density. In this scenario the spin modulation arises due to absorption from the pre-shock accretion flow of the X-ray emitting pole, while the optical radiation is modulated at the orbital side band ($ω_{\rm spin} - Ω_{\rm orbit}$) due to reprocessing in regions within the binary system. Due to its unusual transient behaviour for an intermediate polar, we have also searched for radio signals similar to those observed in the new class of long period transients. We derived upper limits with ASKAP (200--300\,$μ$Jy\,beam$^{-1}$ between 800--1500 MHz) and MWA (40--90\,mJy\,beam$^{-1}$ between 80--300 MHz). △ Less

Submitted 13 July, 2025; v1 submitted 11 July, 2025; originally announced July 2025.

Journal ref: A&A 701, A19 (2025)

Little Red Dots from Small-Scale Primordial Black Hole Clustering

Authors: Borui Zhang, Wei-Xiang Feng, Haipeng An

Abstract: The James Webb Space Telescope (JWST) observations have identified a class of compact galaxies at high redshifts ($4 \lesssim z \lesssim 11$), dubbed "little red dots" (LRDs). The supermassive black holes (SMBHs) of $10^{5-8}{\rm\,M}_{\odot}$ in LRDs favor a heavy-seed origin. We propose a mechanism for their formation: Clusters of primordial black holes, formed through long-short mode coupling on… ▽ More The James Webb Space Telescope (JWST) observations have identified a class of compact galaxies at high redshifts ($4 \lesssim z \lesssim 11$), dubbed "little red dots" (LRDs). The supermassive black holes (SMBHs) of $10^{5-8}{\rm\,M}_{\odot}$ in LRDs favor a heavy-seed origin. We propose a mechanism for their formation: Clusters of primordial black holes, formed through long-short mode coupling on small scales in the early Universe, undergo sequential mergers over extended timescales. This mechanism can evade cosmic microwave background distortions and result in heavy-seed SMBHs via runaway mergers. We employ Monte Carlo simulations to solve the Smoluchowski coagulation equation and determine the runaway merging timescale. The resulting stochastic gravitational wave background offers a distinct signature of this process, and the forming SMBHs can be highly spinning at their formation due to the spin residual of the cluster from tidal fields. This mechanism may explain the rapidly spinning SMBHs in LRDs under the assumption of obscured active galactic nuclei. △ Less

Submitted 22 July, 2025; v1 submitted 9 July, 2025; originally announced July 2025.

Comments: 5 pages, 3 figures, plus supplemental material (2 figures); references updated

GRB 240825A: Early Reverse Shock and Its Physical Implications

Authors: Chao Wu, Yun Wang, Hua-Li Li, Li-Ping Xin, Dong Xu, Benjamin Schneider, Antonio de Ugarte Postigo, Gavin Lamb, Andrea Reguitti, Andrea Saccardi, Xing Gao, Xing-Ling Li, Qiu-Li Wang, Bing Zhang, Jian-Yan Wei, Shuang-Nan Zhang, Frédéric Daigne, Jean-Luc Atteia, Maria-Grazia Bernardini, Hong-bo Cai, Arnaud Claret, Bertrand Cordier, Jin-Song Deng, Olivier Godet, Diego Götz , et al. (62 additional authors not shown)

Abstract: Early multiwavelength observations offer crucial insights into the nature of the relativistic jets responsible for gamma-ray bursts and their interaction with the surrounding medium.We present data of GRB 240825A from 17 space- and ground-based telescopes/instruments, covering wavelengths from NIR/optical to X-ray and GeV, and spanning from the prompt emission to the afterglow phase triggered by S… ▽ More Early multiwavelength observations offer crucial insights into the nature of the relativistic jets responsible for gamma-ray bursts and their interaction with the surrounding medium.We present data of GRB 240825A from 17 space- and ground-based telescopes/instruments, covering wavelengths from NIR/optical to X-ray and GeV, and spanning from the prompt emission to the afterglow phase triggered by Swift and Fermi. The early afterglow observations were carried out by SVOM/C-GFT, and spectroscopic observations of the afterglow by GTC, VLT, and TNG determined the redshift of the burst ($z = 0.659$) later.A comprehensive analysis of the prompt emission spectrum observed by Swift-BAT and Fermi-GBM/LAT reveals a rare and significant high-energy cutoff at ~76 MeV. Assuming this cutoff is due to $γγ$ absorption allows us to place an upper limit on the initial Lorentz factor, $Γ_0 < 245$. The optical/NIR and GeV afterglow light curves be described by the standard external shock model, with early-time emission dominated by a reverse shock (RS) and a subsequent transition to forward shock (FS) emission. Our afterglow modelling yields a consistent estimate of the initial Lorentz factor ($Γ_{\rm 0} \sim 234$). Furthermore, the RS-to-FS magnetic field ratio ($\mathcal{R}_B \sim 302$) indicates that the reverse shock region is significantly more magnetized than the FS region. An isotropic-equivalent kinetic energy of $E_{\text{k,iso}} = 5.25 \times 10^{54}$ erg is derived, and the corresponding $γ$-ray radiation efficiency is estimated to be $η_γ$ = 3.1%. On the other hand, the standard afterglow model can not reproduce the X-ray light curve of GRB 240825A, calling for improved models to characterize all multiwavelength data. △ Less

Submitted 10 August, 2025; v1 submitted 3 July, 2025; originally announced July 2025.

Comments: 31 pages, 9 Figures, 10 Tables

Multi-year Polarimetric Monitoring of Four CHIME-Discovered Repeating Fast Radio Bursts with FAST

Authors: Yi Feng, Yong-Kun Zhang, Jintao Xie, Yuan-Pei Yang, Yuanhong Qu, Dengke Zhou, Di Li, Bing Zhang, Weiwei Zhu, Wenbin Lu, Jiaying Xu, Chenchen Miao, Shiyan Tian, Pei Wang, Ju-Mei Yao, Chen-Hui Niu, Jiarui Niu, Heng Xu, Jinchen Jiang, Dejiang Zhou, Zenan Liu, Chao-Wei Tsai, Zigao Dai, Xuefeng Wu, Fayin Wang , et al. (28 additional authors not shown)

Abstract: In this study, we report multi-year polarization measurements of four repeating FRBs initially discovered by CHIME: FRBs~20190117A, 20190208A, 20190303A, and 20190417A. We observed the four repeating FRBs with FAST, detecting a total of 66 bursts. Two bursts from FRB~20190417A exhibit a circular polarization signal-to-noise ratio greater than 7, with the highest circular polarization fraction reco… ▽ More In this study, we report multi-year polarization measurements of four repeating FRBs initially discovered by CHIME: FRBs~20190117A, 20190208A, 20190303A, and 20190417A. We observed the four repeating FRBs with FAST, detecting a total of 66 bursts. Two bursts from FRB~20190417A exhibit a circular polarization signal-to-noise ratio greater than 7, with the highest circular polarization fraction recorded at 35.7%. While the bursts from FRBs 20190208A and 20190303A are highly linearly polarized, those from FRBs~20190117A and 20190417A show depolarization due to multi-path propagation, with σ_{\mathrm{RM}} = 2.78 \pm 0.05 rad m$^{-2}$ and 5.19 \pm 0.09 rad m$^{-2}$, respectively. The linear polarization distributions among five repeating FRB--FRBs~20190208A, 20190303A, 20201124A, 20220912A, and 20240114A--are nearly identical but show distinct differences from those of non-repeating FRBs. FRBs~20190117A, 20190303A, and 20190417A exhibit substantial rotation measure (RM) variations between bursts, joining other repeating FRBs in this behavior. Combining these findings with published results, 64% of repeating FRBs show RM variations greater than 50 rad m$^{-2}$, and 21\% exhibit RM reversals. A significant proportion of repeating FRBs reside in a dynamic magneto-ionic environment. The structure function of RM variations shows a power-law index of $γ\sim (0-0.8)$, corresponding to a shallow power spectrum $α= -(γ+ 2) \sim -(2.0-2.8)$ of turbulence, if the RM variations are attributed to turbulence. This suggests that the variations are dominated by small-scale RM density fluctuations. We perform K-S tests comparing the RMs of repeating and non-repeating FRBs, which reveal a marginal dichotomy in the distribution of their RMs.We caution that the observed dichotomy may be due to the small sample size and selection biases. △ Less

Submitted 3 July, 2025; originally announced July 2025.

Comments: 17 pages, 5 figures,accepted by SCIENCE CHINA

Multimessenger Emission from Very-High-Energy Black Hole-Jet Systems in the Milky Way

Authors: Jose Carpio, Ali Kheirandish, Bing Zhang

Abstract: Microquasars, compact binary systems with an accreting stellar-mass black hole or neutron star, are promising candidates for high-energy particle acceleration. Recently, the LHAASO collaboration reported on the detection of $>100$ TeV $γ$-ray emission from five microquasars, suggesting that these sources are efficient particle accelerators. In microquasars, high-energy $γ$-rays can be produced in… ▽ More Microquasars, compact binary systems with an accreting stellar-mass black hole or neutron star, are promising candidates for high-energy particle acceleration. Recently, the LHAASO collaboration reported on the detection of $>100$ TeV $γ$-ray emission from five microquasars, suggesting that these sources are efficient particle accelerators. In microquasars, high-energy $γ$-rays can be produced in large-scale jets or winds. In this work, we explore the X-ray, $γ$-ray and neutrino emission from SS 433, V4641 Sgr and GRS 1905+105. We consider leptonic and hadronic scenarios to explain the spectra observed by LHAASO and other high-energy $γ$-ray detectors. We estimate the neutrino flux associated with the hadronic component and investigate the detectability of neutrinos from these sources in current and future neutrino telescopes. We find that among the three sources, V4641 Sgr has the best prospects of observation with a combined next-generation neutrino telescopes. △ Less

Submitted 27 June, 2025; originally announced June 2025.

Microquasar jet-cocoon systems as PeVatrons

Authors: B. Theodore Zhang, Shigeo S. Kimura, Kohta Murase

Abstract: The origin of Galactic cosmic rays (CRs), particularly around the knee region ($\sim$3 PeV), remains a major unsolved question. Recent observations by LHAAASO suggest that the knee is shaped mainly by protons, with a transition to heavier elements at higher energies. Microquasars -- compact jet-emitting sources -- have emerged as possible PeV CR accelerators, especially after detections of ultrahi… ▽ More The origin of Galactic cosmic rays (CRs), particularly around the knee region ($\sim$3 PeV), remains a major unsolved question. Recent observations by LHAAASO suggest that the knee is shaped mainly by protons, with a transition to heavier elements at higher energies. Microquasars -- compact jet-emitting sources -- have emerged as possible PeV CR accelerators, especially after detections of ultrahigh-energy gamma rays from these systems. We propose that the observed proton spectrum (hard below a few PeV, steep beyond) arises from the reacceleration of sub-TeV Galactic CRs via shear acceleration in large-scale microquasar jet-cocoon structures. Our model also naturally explains the observed spectrum of energies around a few tens of PeV by summing up heavier nuclei contributions. Additionally, similar reacceleration processes in radio galaxies can contribute to ultrahigh-energy CRs, bridging Galactic and extragalactic origins. Combined with low-energy CRs from supernova remnants and galaxy clusters around the second knee region, this scenario could provide a unified explanation for CRs across the entire energy spectrum. △ Less

Submitted 25 June, 2025; originally announced June 2025.

Comments: 10 pages, 8 figures

Searching for radio pulsars in old open clusters from the Parkes archive

Authors: S. B. Zhang, J. J. Wei, X. Yang, S. Dai, J. S. Wang, L. Toomey, S. Q. Wang, G. Hobbs, X. F. Wu, L. Staveley-Smith

Abstract: Motivated by the discovery of a pulsar in the direction of the old open cluster NGC 6791, we conducted a search for radio pulsars in archival Parkes observations targeting similar old open clusters. We reprocessed 224 observations totalling 75.02 hours from four clusters: Theia 1661, NGC 6259, Pismis 3, and Trumpler 20. Our analysis identified five known pulsars and three new rotating radio transi… ▽ More Motivated by the discovery of a pulsar in the direction of the old open cluster NGC 6791, we conducted a search for radio pulsars in archival Parkes observations targeting similar old open clusters. We reprocessed 224 observations totalling 75.02 hours from four clusters: Theia 1661, NGC 6259, Pismis 3, and Trumpler 20. Our analysis identified five known pulsars and three new rotating radio transient (RRAT) candidates. By comparing the measured dispersion measures (DMs) with the expected DM values for each cluster derived from YMW16 and NE2001 models, we conclude that most detected sources are likely background pulsars. However, RRAT J1749-25 in Theia 1661 and RRAT J1237-60 in Trumpler 20 have DMs reasonably close to their respective clusters, suggesting possible membership. The association between PSR J1750-2536 and Theia 1661 remains ambiguous due to its intermediate DM. These candidate cluster-associated neutron stars warrant follow-up with more sensitive telescopes such as MeerKAT or the SKA, potentially offering valuable insights into neutron star retention mechanisms and evolution in open cluster environments. △ Less

Submitted 23 June, 2025; originally announced June 2025.

Comments: 9 pages, 3 figures, 2 tables, accept for publication in ApJ

A Fast Bayesian Method for Coherent Gravitational Wave Searches with Relative Astrometry

Authors: Benjamin Zhang, Kris Pardo, Yijun Wang, Luke Bouma, Tzu-Ching Chang, Olivier Doré

Abstract: Using relative stellar astrometry for the detection of coherent gravitational wave sources is a promising method for the microhertz range, where no dedicated detectors currently exist. Compared to other gravitational wave detection techniques, astrometry operates in an extreme high-baseline-number and low-SNR-per-baseline limit, which leads to computational difficulties when using conventional Bay… ▽ More Using relative stellar astrometry for the detection of coherent gravitational wave sources is a promising method for the microhertz range, where no dedicated detectors currently exist. Compared to other gravitational wave detection techniques, astrometry operates in an extreme high-baseline-number and low-SNR-per-baseline limit, which leads to computational difficulties when using conventional Bayesian search techniques. We extend a technique for efficiently searching pulsar timing array datasets through the precomputation of inner products in the Bayesian likelihood, showing that it is applicable to astrometric datasets. Using this technique, we are able to reduce the total dataset size by up to a factor of $\mathcal{O}(100)$, while remaining accurate to within 1% over two orders of magnitude in gravitational wave frequency. Applying this technique to simulated astrometric datasets for the Kepler Space Telescope and Nancy Grace Roman Space Telescope missions, we obtain forecasts for the sensitivity of these missions to coherent gravitational waves. Due to the low angular sky coverage of astrometric baselines, we find that coherent gravitational wave sources are poorly localized on the sky. Despite this, from $10^{-8}$ Hz to $10^{-6}$ Hz, we find that Roman is sensitive to coherent gravitational waves with an instantaneous strain above $h_0 \simeq 10^{-11.4}$, and Kepler is sensitive to strains above $h_0 \simeq $ $10^{-12.4}$. At this strain, we can detect a source with a frequency of $10^{-7}$ Hz and a chirp mass of $10^9$ $M_\odot$ at a luminosity distance of 3.6 Mpc for Kepler, and 0.3 Mpc for Roman. △ Less

Submitted 23 June, 2025; originally announced June 2025.

Comments: 14 pages, 5 figures

Validating the bright Gaia celestial reference frame with new VLBI astrometry of radio stars

Authors: Jingdong Zhang, Bo Zhang, Shuangjing Xu, Xiaofeng Mai

Abstract: There exist inconsistencies between the bright and faint Gaia Celestial Reference Frame 3 (Gaia-CRF3), which manifests as a systematic rotation and needs to be independently estimated then corrected in future data releases. We collected 64 radio stars with VLBI astrometry, of which 16 have new VLBI observations with reference epochs close to Gaia. We estimated the orientation and spin biases of th… ▽ More There exist inconsistencies between the bright and faint Gaia Celestial Reference Frame 3 (Gaia-CRF3), which manifests as a systematic rotation and needs to be independently estimated then corrected in future data releases. We collected 64 radio stars with VLBI astrometry, of which 16 have new VLBI observations with reference epochs close to Gaia. We estimated the orientation and spin biases of the bright Gaia-CRF3 by comparing VLBI radio star astrometry with their Gaia DR3 counterparts. We also attempted to estimate orientation by utilizing the a priori magnitude-dependent spin parameters derived from Gaia internal estimation. Our independent estimation of the orientation at G<10.5 is [-15\pm119, +330\pm139,+218\pm109] uas (J2016.0), and the spin ([+21\pm18, +52\pm20,-7\pm20] uas/yr) agrees with Gaia internal estimation within 1-sigma range. The orientation-only estimation suggests that the orientation bias of the bright Gaia-CRF3 may also be magnitude-dependent. △ Less

Submitted 14 July, 2025; v1 submitted 23 June, 2025; originally announced June 2025.

Comments: Accepted for publication in A&A

Journal ref: A&A 699, A345 (2025)

Exploring the Link between Fast Radio Burst and Binary Neutron Star Origins with Spaceborne Gravitational Wave Observations

Authors: Yu-xuan Yin, En-kun Li, Bing Zhang, Yi-Ming Hu

Abstract: The origin of repeating Fast Radio Bursts (FRBs) is an open question, with observations suggesting that at least some are associated with old stellar populations. It has been proposed that some repeating FRBs may be produced by interactions of the binary neutron star magnetospheres decades to centuries before the coalescence. These systems would also emit centi-Hertz gravitational waves during thi… ▽ More The origin of repeating Fast Radio Bursts (FRBs) is an open question, with observations suggesting that at least some are associated with old stellar populations. It has been proposed that some repeating FRBs may be produced by interactions of the binary neutron star magnetospheres decades to centuries before the coalescence. These systems would also emit centi-Hertz gravitational waves during this period, which can be detectable by space-borne gravitational wave detectors. We explore the prospects of using current and future space-borne gravitational wave detectors, such as TianQin, LISA, and DECIGO, to test this FRB formation hypothesis. Focusing on nearby galaxies like M81, which hosts a repeating FRB source in a globular cluster, we calculate the detection capabilities for binary neutron star systems. Our analysis reveals that while missions like TianQin and LISA face limitations in horizon distance, changing detector pointing direction could significantly enhance detection probabilities. Considering the chance of a Milky Way-like galaxy coincidentally containing a BNS within 100 years before merger is only $3\times10^{-5}$ to $5\times10^{-3}$, if a signal is detected originating from M81, we can establish the link between FRB and binary neutron stars with a significance level of at least 2.81$σ$, or a Bayes factor of $4\times10^6 - 7\times10^8$ / $5\times10^2 - 10^5$ against the background model with optimistic/realistic assumptions. Next-generation detectors such as DECIGO offer enhanced capabilities and should easily detect these systems in M81 and beyond. Our work highlights the critical role of space-borne gravitational wave missions in unraveling FRB origins. △ Less

Submitted 17 June, 2025; v1 submitted 14 June, 2025; originally announced June 2025.

Comments: The Astrophysical Journal Letters, Volume 985, Number 2

Searching for radio pulses from radio-quiet gamma-ray pulsars with FAST

Authors: S. Q. Wang, S. Dai, N. Wang, A. Zic, G. Hobbs, D. Li, R. B. Ding, L. Peng, Z. C. Pan, S. B. Zhang

Abstract: We present periodicity and single-pulse searches at 1250 MHz for 22 radio-quiet gamma-ray pulsars, conducted using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). For PSR J1813$-$1246, we successfully detected pulsed signals with a spin period of 48.08 ms and a dispersion measure of 209.85 ${\rm pc cm^{-3}}$, consistent with the spin period measured at gamma-ray wavelengths. The… ▽ More We present periodicity and single-pulse searches at 1250 MHz for 22 radio-quiet gamma-ray pulsars, conducted using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). For PSR J1813$-$1246, we successfully detected pulsed signals with a spin period of 48.08 ms and a dispersion measure of 209.85 ${\rm pc cm^{-3}}$, consistent with the spin period measured at gamma-ray wavelengths. The estimated flux density is approximately 9 $μ$Jy. For the remaining 21 sources, no radio emission was detected, with flux density upper limits of several $ μ$Jy. The capability to detect pulsars with such low flux densities provides the opportunity to determine if and how these faint sources differ from much radio-brighter pulsars. △ Less

Submitted 12 June, 2025; originally announced June 2025.

Comments: 11 pages, 4 figures, Accepted for publication in ApJ

Topological defects as effective dynamical dark energy

Authors: Haipeng An, Chengcheng Han, Borui Zhang

Abstract: In this work, we consider the possibility that the dynamical dark energy hinted at by recent DESI data may be mimicked by the effects of additional components in the universe, potentially arising from topological defects. We find that the data does not show a particular preference for the existence of cosmic strings. However, a domain wall contribution at the percent level can improve the fit, yie… ▽ More In this work, we consider the possibility that the dynamical dark energy hinted at by recent DESI data may be mimicked by the effects of additional components in the universe, potentially arising from topological defects. We find that the data does not show a particular preference for the existence of cosmic strings. However, a domain wall contribution at the percent level can improve the fit, yielding a $Δχ^2= -1.72$ compared to the $Λ\rm{CDM}$ model. The improvement indicates that topological defects remain a viable and interesting extension to $Λ\rm{CDM}$, meriting further investigation with future cosmological data. △ Less

Submitted 11 June, 2025; originally announced June 2025.