Showing 1–50 of 330 results for author: Gao, H

The Head-on Collision of a Neutron Star with a White Dwarf

Authors: Zong-kai Peng, He Gao, Xian-Fei Zhang

Abstract: We have computed the physical processes involved in a head-on collision between a neutron star (NS) and a white dwarf (WD). The outcomes of such collisions vary depending on the mass and type of the WD. We have separately examined the dynamical processes for collisions between NSs and helium WDs (He-WDs), carbon-oxygen WDs (CO-WDs), and oxygen-neon WDs (ONe-WDs). We aim to investigate whether the… ▽ More We have computed the physical processes involved in a head-on collision between a neutron star (NS) and a white dwarf (WD). The outcomes of such collisions vary depending on the mass and type of the WD. We have separately examined the dynamical processes for collisions between NSs and helium WDs (He-WDs), carbon-oxygen WDs (CO-WDs), and oxygen-neon WDs (ONe-WDs). We aim to investigate whether the collision can trigger a thermonuclear explosion of the WD, and if not, whether the NS can remain bound within the WD to form a Thorne-Zytkow-like object (TZlO). For a thermonuclear explosion to occur, at least two conditions must be satisfied: (i) the collision-induced temperature must reach the ignition threshold of the relevant nuclear reactions, and (ii) the burning material must remain in a degenerate state. For different types of WDs, there exist parameter ranges where both conditions are fulfilled, implying that NS-WD collisions can indeed induce thermonuclear explosions, leading to sub-Chandrasekhar Type Ia supernovae or other exotic optical transients powered by thermonuclear explosion. On the other hand, the formation of a TZlO requires that the WD material exerts sufficient drag on the NS to prevent its escape, while the interaction must not trigger a thermonuclear explosion of the WD. Our results indicate that such conditions can be realized in the case of low-mass CO-WDs and low-mass ONe-WDs, provided that the viscous coefficient is sufficiently large. △ Less

Submitted 8 December, 2025; originally announced December 2025.

Comments: 12 pages, 4 figures, accepted for publication in ApJ

Normal or transitional? The evolution and properties of two type Ia supernovae in the Virgo cluster

Authors: L. Izzo, C. Gall, N. Khetan, N. Earl, J. Hjorth, W. B. Hoogendam, Y. Q. Ni, A. Sedgewick, S. M. Ward, Y. Zenati, K. Auchettl, S. Bhattacharjee, S. Benetti, M. Branchesi, E. Cappellaro, A. Catapano, K. C. Chambers, D. A. Coulter, K. W. Davis, M. Della Valle, S. Dhawan, T. de Boer, G. Dimitriadis, R. J. Foley, M. Fulton , et al. (25 additional authors not shown)

Abstract: Type Ia supernovae (SNe Ia) are among the most precise cosmological distance indicators used to study the expansion history of the Universe. The vast increase of SN Ia data due to large-scale astrophysical surveys has led to the discovery of a wide variety of SN Ia sub-classes, such as transitional and fast-declining SNe Ia. However, their distinct photometric and spectroscopic properties differen… ▽ More Type Ia supernovae (SNe Ia) are among the most precise cosmological distance indicators used to study the expansion history of the Universe. The vast increase of SN Ia data due to large-scale astrophysical surveys has led to the discovery of a wide variety of SN Ia sub-classes, such as transitional and fast-declining SNe Ia. However, their distinct photometric and spectroscopic properties differentiate them from the population of normal SNe Ia such that their use as cosmological tools remains challenged. Here, we present a high-cadenced photometric and spectroscopic dataset of two SNe Ia, SNe 2020ue and 2020nlb, which were discovered in the nearby Virgo cluster of galaxies. Our study shows that SN 2020nlb is a normal SN Ia whose unusually red color is intrinsic, arising from a lower photospheric temperature rather than interstellar reddening, providing clear evidence that color diversity among normal SNe Ia can have a physical origin. In contrast, SN 2020ue has photometric properties, such as color evolution and light-curve decay rate, similar to those of transitional SNe, spectroscopically it is more aligned with normal SNe Ia. This is evident from spectroscopic indicators such as the pseudo-equivalent width of \ion{Si}{II} lines. Thus, such SNe Ia that are photometrically at the edge of the standard normal SNe Ia range may be missed in cosmological SNe Ia samples. Our results highlight that spectroscopic analysis of SNe Ia around peak brightness is crucial for identifying intrinsic color variations and constructing a more complete and physically homogeneous SN Ia sample for precision cosmology. △ Less

Submitted 29 November, 2025; originally announced December 2025.

Comments: 24 pages, 21 figures, 7 tables. Accepted for publication in A&A

Constraining the Properties of GRB Accreting Magnetar with $R/I$ Evolutionary Effects Using \emph{Swift}/XRT Data

Authors: Lin Lan, He Gao, Litao Zhao, Shunke Ai, Jie Lin, Long Li, Lang Xie, Li-Ping Xin, Jian-Yan Wei

Abstract: A newly born millisecond magnetar has been proposed as one possible central engine of some long gamma-ray bursts (LGRBs) with X-ray plateau. In this work, we used a universal correlation between initial spin period ($P_0$) and surface magnetic field ($B_p$) of newborn magnetar based on an LGRB sample in \cite{Lan2025} to explore the propeller properties of accreting magnetar with $R/I$ evolutionar… ▽ More A newly born millisecond magnetar has been proposed as one possible central engine of some long gamma-ray bursts (LGRBs) with X-ray plateau. In this work, we used a universal correlation between initial spin period ($P_0$) and surface magnetic field ($B_p$) of newborn magnetar based on an LGRB sample in \cite{Lan2025} to explore the propeller properties of accreting magnetar with $R/I$ evolutionary effects. We found that $B_p-P_0$ relation is approximately consistent with $B_p\propto P_{\rm eq}^{7/6}$. Here, $P_{\rm eq}$ is equilibrium spin period in magnetic propeller model. The $B_p-P_0$ relation indicates that $P_0$ may not be true initial spin period of newborn magnetar, but had reached an equilibrium spin period via fallback accretion in propeller model. The magnetar accretion rate in our LGRBs is in range of $\dot{M}\sim10^{-5}-10^{-2} M_{\odot} \rm s^{-1}$ by incorporating $R/I$ evolutionary effects, and using the transition relation between gravitational mass $M_g$ and baryonic mass $M_b$ in different equation of states. Such accretion rates ensure that the accreting magnetars in our sample survive until reaching the equilibrium spin period, and the accretion rate is one order of magnitude lower compared to the statistical results in \cite{Stratta2018} and \cite{Linweili2020}, which used constant $R/I/M_g$ scenario. We suggested that adopting a constant $R/I/M_g$ scenario for modeling propeller regime in accreting magnetar results in a higher mass accretion rate, which may impair our understanding of the physical nature and its surroundings of accreting magnetar, and low-metallicity progenitors can provide enough material to satisfy the accretion requirements of newborn accreting magnetar in LGRBs. △ Less

Submitted 27 November, 2025; originally announced November 2025.

Comments: 22 pages, 6 figures, and 2 tables. Accepted for publication in ApJ

GRB 240715A: Revealing Novel Intrinsic Mechanism by Different Individual Pulse

Authors: Wen-Jun Tan, Chen-Wei Wang, Shao-Lin Xiong, Shi-Jie Zheng, Jiang He, Xiao-Yun Zhao, Yue Huang, Shu-Xu Yi, Bing Li, He Gao, Bo-bing Wu, Bing Zhang, Frederic Daigne, Maria-Grazia Bernardini, Bin-Bin Zhang, Stephane Basa, Bertrand Cordier, Jin-Song Deng, Yong-Wei Dong, Damien Dornic, Olivier Godet, Xu-Hui Han, Mao-Hai Huang, Cyril Lachaud, Hua-Li Li , et al. (15 additional authors not shown)

Abstract: The Space-based multiband astronomical Variable Objects Monitor (SVOM), detected its first short gamma-ray burst, GRB 240715A, in-flight, which was jointly observed by Fermi. Based on observational data of SVOM/GRM and Fermi/GBM, we perform a comprehensive temporal and spectral analysis for individual pulse in the prompt emission of this burst, and novel characteristics are revealed. Firstly, oppo… ▽ More The Space-based multiband astronomical Variable Objects Monitor (SVOM), detected its first short gamma-ray burst, GRB 240715A, in-flight, which was jointly observed by Fermi. Based on observational data of SVOM/GRM and Fermi/GBM, we perform a comprehensive temporal and spectral analysis for individual pulse in the prompt emission of this burst, and novel characteristics are revealed. Firstly, opposite evolutions of spectral lag are found in the first and third pulse of this burst. Second, the large negative lag of the first pulse is an outlier in short GRB sample, especially when the pulse duration is considered. Spectral analysis shows that the negative lag of the first pulse is caused by the evolution of spectrum index, and is irrelevant to Epeak, which is inconsistent with the previous study. The intrinsic mechanism is probably attributed to electron cooling in the decaying magnetic field, which leads to the continuous hardening of the spectrum index and results in negative lag. Furthermore, spectral analysis also shows that the third pulse is more likely to be described by a quasi-thermal spectrum, indicating the existence of photospheric emission. It is difficult to explain how the synchrotron radiation appears before photospheric emission in a single GRB and some assumptions are discussed. △ Less

Submitted 23 November, 2025; originally announced November 2025.

Comments: 21 pages, 4 figures, accepted by The Astrophysical Journal Letters

Characterization of type Ibn SNe

Authors: D. Farias, C. Gall, V. A. Villar, K. Auchettl, K. M. de Soto, A. Gagliano, W. B. Hoogendam, G. Narayan, A. Sedgewick, S. K. Yadavalli, Y. Zenati, C. R. Angus, K. W. Davis, J. Hjorth, W. V. Jacobson-Galán, D. O. Jones, C. D. Kilpatrick, M. J. Bustamante Rosell, D. A. Coulter, G. Dimitriadis, R. J. Foley, A. Gangopadhyay, H. Gao, M. E. Huber, L. Izzo , et al. (7 additional authors not shown)

Abstract: Type Ibn supernovae (SNe) are characterized by narrow helium (He I) lines from photons produced by the unshocked circumstellar material (CSM). About 80 SNe Ibn have been discovered to date, and only a handful have extensive observational records. Thus, many open questions regarding the progenitor system and the origin of the CSM remain. Here we investigate potential correlations between the spectr… ▽ More Type Ibn supernovae (SNe) are characterized by narrow helium (He I) lines from photons produced by the unshocked circumstellar material (CSM). About 80 SNe Ibn have been discovered to date, and only a handful have extensive observational records. Thus, many open questions regarding the progenitor system and the origin of the CSM remain. Here we investigate potential correlations between the spectral features of the prominent He I $λ$5876 line and the optical and X-ray light curve properties of SNe Ibn. We compile the largest sample of 61 SNe Ibn to date, of which 24 SNe have photometric and spectroscopic data from the Young Supernova Experiment and 37 SNe have archival data sets. We fit 24 SNe Ibn with sufficient photometric coverage ($B$ to $z$ bands) using semi-analytical models from MOSFiT. We demonstrate that the light curves of SNe Ibn are more diverse than previous analyses suggest, with absolute $r$-band peak magnitudes of $-19.4\pm0.6$~mag and rise (from $-10$ days to peak) and decay-rates (from peak to +10 days) of $-0.08\pm0.06$ and $0.08\pm0.03$ mag/day, respectively. We find that the majority of SNe Ibn in the sub-sample are consistent with a low-energy explosion ($<10^{51}$ erg) of a star with a compact envelope surrounded by $\sim$0.1 M$_{\odot}$ of helium-rich CSM. The inferred ejecta masses are small ($\sim 1$ M$_{\odot}$) and expand with a velocity of $\sim$5000 km/s. Our spectroscopic analysis shows that the mean velocity of the narrow component of the He I lines, associated to the CSM, peaks at $\sim1100$ km/s. The mean CSM and ejecta masses inferred for a sub-sample of SNe Ibn indicate that their progenitors are not massive ($\sim10$ M$_{\odot}$), single stars at the moment of explosion, but are likely binary systems. This agrees with the detection of potential companion stars of SNe Ibn progenitors, and the inferred CSM properties from stellar evolution models. △ Less

Submitted 15 November, 2025; originally announced November 2025.

Comments: 25 pages, 13 figures, 7 tables

Modeling the Multi-Wavelength Afterglow of Short Gamma-Ray Bursts with a Plateau Phase

Authors: Chen Deng, Yong-Feng Huang, Abdusattar Kurban, Jin-Jun Geng, Fan Xu, Xiao-Fei Dong, Hao-Xuan Gao, En-Wei Liang, Liang Li

Abstract: Short gamma-ray bursts (GRBs) exhibiting a plateau phase provide valuable insights into the post-merger activity of their central engines. Although the physical origin of the plateau remains uncertain, the magnetar energy injection model offers a compelling explanation that reproduces the observed temporal and luminosity features. However, previous studies relying solely on X-ray data have suffere… ▽ More Short gamma-ray bursts (GRBs) exhibiting a plateau phase provide valuable insights into the post-merger activity of their central engines. Although the physical origin of the plateau remains uncertain, the magnetar energy injection model offers a compelling explanation that reproduces the observed temporal and luminosity features. However, previous studies relying solely on X-ray data have suffered from strong parameter degeneracies when constraining the magnetar parameters. Here we perform broadband afterglow modeling on seven short GRBs with plateau features by combining X-ray, optical, and radio observations within the framework of the magnetar energy injection model. Key model parameters are derived by using the Markov Chain Monte Carlo method. It is found that the energy injection substantially modifies the afterglow dynamics in most events. Compared with X-ray--only analyses, our broadband modeling yields systematically a lower magnetic field strength and a shorter spin period for the central magnetar, corresponding to a higher injection luminosity. The study clearly shows that incorporating multi-wavelength data effectively alleviates the degeneracy between the magnetar parameters and X-ray radiative efficiency. In addition, the distribution of our short GRBs differs markedly from long GRBs when they are plotted on the initial Lorentz factor versus gamma-ray energy plane. This offset, consistent with the observed harder spectrum of short GRBs, may serve as a useful diagnostic for investigating the progenitor as larger samples are available. △ Less

Submitted 14 November, 2025; originally announced November 2025.

Comments: 19 pages, 6 figures, 1 table

An axisymmetric shock breakout indicated by prompt polarized emission from the type II supernova 2024ggi

Authors: Yi Yang, Xudong Wen, Lifan Wang, Dietrich Baade, J. Craig Wheeler, Alexei V. Filippenko, Avishay Gal-Yam, Justyn Maund, Steve Schulze, Xiaofeng Wang, Chris Ashall, Mattia Bulla, Aleksandar Cikota, He Gao, Peter Hoeflich, Gaici Li, Divya Mishra, Ferdinando Patat, Kishore C. Patra, Sergiy S. Vasylyev, Shengyu Yan

Abstract: The death of massive stars is triggered by an infall-induced bounce shock that disrupts the star. How such a shock is launched and propagates through the star is a decade-long puzzle. Some models assume that the shock can be reenergized by absorbing neutrinos, leading to highly aspherical explosions. Other models involve jet-powered shocks that lead to bipolar explosions reflected in the geometry… ▽ More The death of massive stars is triggered by an infall-induced bounce shock that disrupts the star. How such a shock is launched and propagates through the star is a decade-long puzzle. Some models assume that the shock can be reenergized by absorbing neutrinos, leading to highly aspherical explosions. Other models involve jet-powered shocks that lead to bipolar explosions reflected in the geometry of the shock-breakout emission. We report measurement of the geometry of the shock breakout through unprecedentedly early spectropolarimetry of the nearby type II supernova 2024ggi starting ~1.2 days after the explosion. The measurement indicates a well-defined symmetry axis of the shock breakout, which is also shared by the hydrogen-rich envelope that emerged after the circumstellar matter was engulfed by the ejecta, revealing a persisting and prominent symmetry axis throughout the explosion. These findings suggest that the physical mechanism driving the explosion of massive stars manifests a well-defined axial symmetry and acts on large scales. △ Less

Submitted 11 November, 2025; originally announced November 2025.

Comments: Science Advances: https://www.science.org/doi/10.1126/sciadv.adx2925 ESO PR: https://www.eso.org/public/news/eso2520/

Spectral Diversity in Type Ibn Supernovae and the Large Host Offset of SN2024acyl

Authors: Yize Dong, V. Ashley Villar, Anya Nugent, Griffin Hosseinzadeh, Ryan J. Foley, Christa Gall, Monica Gallegos-Garcia, Conor Ransome, Aidan Sedgewick, Daichi Tsuna, Stefano Valenti, Henna Abunemeh, Moira Andrews, Katie Auchettl, K. Azalee Bostroem, David A. Coulter, Thomas de Boer, Kaylee de Soto, Diego A. Farias, Joseph Farah, Danielle Frostig, Hua Gao, Alex Gagliano, Emily Hoang, D. Andrew Howell , et al. (13 additional authors not shown)

Abstract: In this paper, we first present observations of SN~2024acyl, a normal Type Ibn supernova with a large projected offset ($\sim$35~kpc) from its host galaxy. The low star-formation rate measured at the explosion site raises the possibility that the progenitor of SN~2024acyl may not have been a massive star. We then examine, more broadly, the spectral diversity of Type Ibn supernovae around 20--35 da… ▽ More In this paper, we first present observations of SN~2024acyl, a normal Type Ibn supernova with a large projected offset ($\sim$35~kpc) from its host galaxy. The low star-formation rate measured at the explosion site raises the possibility that the progenitor of SN~2024acyl may not have been a massive star. We then examine, more broadly, the spectral diversity of Type Ibn supernovae around 20--35 days after peak brightness and identify two distinct groups: Group I, which shows bluer rest-frame optical color and narrower He~I emission lines; and Group II, which shows redder rest-frame optical color and broader He~I lines. Group~I also tends to show higher peak luminosities. The diversity we identify appears to be closely connected to the diversity observed around peak and to persist into late phases ($>80$ days after peak). Given its redder color and broader He~I lines, we classify SN~2024acyl as belonging to Group II. Based on the current dataset, we find no clear connection between this spectral diversity and either the host environments of Type Ibn SNe or their pre-explosion activity. The observed diversity in Type Ibn SNe likely reflects differences in circumstellar material properties and/or explosion energetics. These differences could result from a range of progenitor properties, such as different helium star mass, orbital period and companion type if they are in binary systems, and may indicate fundamentally diverse progenitors. Whether a continuous distribution exists between the two groups remains to be determined and will require further data to explore. △ Less

Submitted 9 November, 2025; v1 submitted 5 November, 2025; originally announced November 2025.

Comparative Statistical Analysis of Prompt and Afterglow X-Ray Flares in Gamma-Ray Bursts: Insights into Extended Central Engine Activity

Authors: Yinuo Ma, He Gao

Abstract: Gamma-ray bursts (GRBs) are the most energetic phenomena in the Universe, characterized by prompt gamma-ray emission followed by multiwavelength afterglows. X-ray flares, observed during the afterglow phase, are generally believed to originate from the prolonged activity of the central engine, though direct evidence has been scarce. In this study, we present a comprehensive statistical analysis of… ▽ More Gamma-ray bursts (GRBs) are the most energetic phenomena in the Universe, characterized by prompt gamma-ray emission followed by multiwavelength afterglows. X-ray flares, observed during the afterglow phase, are generally believed to originate from the prolonged activity of the central engine, though direct evidence has been scarce. In this study, we present a comprehensive statistical analysis of X-ray flares from 315 GRBs observed by the Swift/X-ray Telescope over nearly two decades. We categorize flares into prompt flares (occurring during the prompt emission phase) and afterglow flares and compare their temporal and luminosity properties. Our analysis reveals that both types of flares exhibit similar morphological characteristics, with prompt flares being brighter and occurring earlier than afterglow flares. We find strong correlations between flare parameters, such as peak time, duration, and luminosity, which follow consistent patterns across both flare types. These findings suggest that X-ray flares, regardless of their timing, share a common origin in the central engine's activity. Our results imply that the central engine's activity duration extends beyond the prompt gamma-ray emission phase, highlighting the importance of considering X-ray flares when studying GRB progenitors and central engine properties. This work provides robust statistical evidence supporting the central engine origin of X-ray flares and underscores the need for future observations with missions like the Space-based multi-band astronomical Variable Objects Monitor and Einstein Probe to further elucidate the nature of GRB central engines. △ Less

Submitted 21 October, 2025; originally announced October 2025.

Comments: 15 pages, 12 figures, published in ApJ

Journal ref: The Astrophysical Journal, 989:113 (15pp), 2025 August 10

A Common Synchrotron Origin for Prompt Gamma-Ray and Soft X-Ray Emission in GRBs: Evidence from Joint Spectral Analysis

Authors: Ziming Wang, Chenyu Wang, He Gao, Hua Feng, An Li, Lin Lin, Songyu Shen

Abstract: The recent launches of the Einstein Probe (EP) and the Space Variable Objects Monitor (SVOM) mission have led to the detection of a growing number of long GRBs with significant, early soft X-ray flux during their gamma-ray emission, prompting the question of whether their multi-band prompt emission shares a common origin in region and mechanism. To address this, we utilize the 20-year Swift archiv… ▽ More The recent launches of the Einstein Probe (EP) and the Space Variable Objects Monitor (SVOM) mission have led to the detection of a growing number of long GRBs with significant, early soft X-ray flux during their gamma-ray emission, prompting the question of whether their multi-band prompt emission shares a common origin in region and mechanism. To address this, we utilize the 20-year Swift archival data, which provides a substantial sample of joint soft X-ray and gamma-ray observations, enabling a systematic joint spectral study. We resolve 110 temporal pulses from 46 GRBs and find that a single power-law model with a low-energy break or cutoff adequately describes the prompt spectra from 150 keV down to 0.5 keV. More than half of the sample pulses require a break around a few keV, with average spectral indices $\langle α_1 \rangle = -0.88$ and $\langle α_2 \rangle = -1.46$ consistent with synchrotron radiation in a marginally fast-cooling regime. The observed spectral evolution and the distribution of indices support a single-emission-region origin, where the varying spectral shapes are largely governed by the evolution of the synchrotron cooling frequency $ν_c$ and the effect of finite emission width. The observed differences in the temporal behavior between X-ray and gamma-ray light curves can be naturally explained by this spectral evolution across the broad band. △ Less

Submitted 20 October, 2025; originally announced October 2025.

Comments: 25 pages, 24 figures

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

Authors: Dongyue Li, Wenda Zhang, Jun Yang, Jin-Hong Chen, Weimin Yuan, Huaqing Cheng, Fan Xu, Xinwen Shu, Rong-Feng Shen, Ning Jiang, Jiazheng Zhu, Chang Zhou, Weihua Lei, Hui Sun, Chichuan Jin, Lixin Dai, Bing Zhang, Yu-Han Yang, Wenjie Zhang, Hua Feng, Bifang Liu, Hongyan Zhou, Haiwu Pan, Mingjun Liu, Stephane Corbel , et al. (75 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 23 December, 2025; v1 submitted 30 September, 2025; originally announced September 2025.

Comments: submitted on 19 October 2025, accepted for publication in Science Bulletin on 12 December 2025

The Hubble Tension resolved by the DESI Baryon Acoustic Oscillations Measurements

Authors: X. D. Jia, J. P. Hu, D. H. Gao, S. X. Yi, F. Y. Wang

Abstract: The $Λ$ cold dark matter ($Λ$CDM) cosmological model provides a good description of a wide range of astrophysical and cosmological observations. However, severe challenges to the phenomenological $Λ$CDM model have emerged recently, including the Hubble constant tension and the significant deviation from the $Λ$CDM model reported by the Dark Energy Spectroscopic Instrument (DESI) collaboration. Des… ▽ More The $Λ$ cold dark matter ($Λ$CDM) cosmological model provides a good description of a wide range of astrophysical and cosmological observations. However, severe challenges to the phenomenological $Λ$CDM model have emerged recently, including the Hubble constant tension and the significant deviation from the $Λ$CDM model reported by the Dark Energy Spectroscopic Instrument (DESI) collaboration. Despite many explanations for the two challenges have been proposed, the origins of them are still intriguing mysteries. Here, we investigate the DESI Baryon Acoustic Oscillations (BAOs) measurements to interpret the Hubble constant tension. Employing a non-parametric method, we find that the dark energy equation of state $w(z)$ evolves with redshift from DESI BAO data and type Ia supernovae. From the Friedmann equations, the Hubble constant ($H_0$) is derived from $w(z)$ model-independently. We find that the values of $H_0$ show a descending trend as a function of redshift, and can effectively resolve the Hubble constant tension. Our study finds that the two unexpected challenges to the $Λ$CDM model can be understood in one physical framework, e.g., dynamical dark energy. △ Less

Submitted 7 November, 2025; v1 submitted 22 September, 2025; originally announced September 2025.

Comments: 15 pages, 6 figures, 2 tables. Accepted by ApJL

The radio flare and multi-wavelength afterglow of the short GRB 231117A: energy injection from a violent shell collision

Authors: G. E. Anderson, G. P. Lamb, B. P. Gompertz, L. Rhodes, A. Martin-Carrillo, A. J. van der Horst, A. Rowlinson, M. E. Bell, T. -W. Chen, H. M. Fausey, M. Ferro, P. J. Hancock, S. R. Oates, S. Schulze, R. L. C. Starling, S. Yang, K. Ackley, J. P. Anderson, A. Andersson, J. F. Agüí Fernández, R. Brivio, E. Burns, K. C. Chambers, T. de Boer, V. D'Elia , et al. (42 additional authors not shown)

Abstract: We present the early radio detection and multi-wavelength modeling of the short gamma-ray burst (GRB) 231117A at redshift $z=0.257$. The Australia Telescope Compact Array automatically triggered a 9-hour observation of GRB 231117A at 5.5 and 9 GHz following its detection by the Neil Gehrels Swift Observatory just 1.3 hours post-burst. Splitting this observation into 1-hour time bins, the early rad… ▽ More We present the early radio detection and multi-wavelength modeling of the short gamma-ray burst (GRB) 231117A at redshift $z=0.257$. The Australia Telescope Compact Array automatically triggered a 9-hour observation of GRB 231117A at 5.5 and 9 GHz following its detection by the Neil Gehrels Swift Observatory just 1.3 hours post-burst. Splitting this observation into 1-hour time bins, the early radio afterglow exhibited flaring, scintillating and plateau phases. The scintillation allowed us to place the earliest upper limit ($<10$ hours) on the size of a GRB blast wave to date, constraining it to $<1\times10^{16}$ cm. Multi-wavelength modeling of the full afterglow required a period of significant energy injection between $\sim 0.02$ and $1$ day. The energy injection was modeled as a violent collision of two shells: a reverse shock passing through the injection shell explains the early radio plateau, while an X-ray flare is consistent with a shock passing through the leading impulsive shell. Beyond 1 day, the blast wave evolves as a classic decelerating forward shock with an electron distribution index of $p=1.66\pm0.01$. Our model also indicates a jet-break at $\sim2$ days, and a half-opening angle of $θ_j=16\mathring{.}6 \pm 1\mathring{.}1$. Following the period of injection, the total energy is $ζ\sim18$ times the initial impulsive energy, with a final collimation-corrected energy of $E_{\mathrm{Kf}}\sim5.7\times10^{49}$ erg. The minimum Lorentz factors this model requires are consistent with constraints from the early radio measurements of $Γ>35$ to $Γ>5$ between $\sim0.1$ and $1$ day. These results demonstrate the importance of rapid and sensitive radio follow-up of GRBs for exploring their central engines and outflow behaviour. △ Less

Submitted 20 August, 2025; originally announced August 2025.

Comments: 34 pages, 10 figures, submitted to ApJ

The New Status Qvo? SN 2021qvo is Another 2003fg-like Type Ia Supernova with a Rising Light-Curve Bump

Authors: I. A. Abreu Paniagua, W. B. Hoogendam, D. O. Jones, G. Dimitriadis, R. J. Foley, C. Gall, J. O'Brien, K. Taggart, C. R. Angus, C. Ashall, K. Auchettl, D. A. Coulter, K. W. Davis, T. de Boer, A. Do, H. Gao, L. Izzo, C. -C. Lin, T. B. Lowe, Z. Lai, R. Kaur, M. Y. Kong, A. Rest, M. R. Siebert, S. K. Yadavalli , et al. (2 additional authors not shown)

Abstract: In recent years, multiple Type Ia supernovae (SNe Ia) have been observed with ''bumps'' in their rising light curves shortly after explosion. Here, we present SN 2021qvo: a SN Ia that exhibits a clear early bump in photometry obtained by the Young Supernova Experiment. Photometric and spectroscopic observations of SN 2021qvo show that it has a broader light curve, higher peak luminosity, shallower… ▽ More In recent years, multiple Type Ia supernovae (SNe Ia) have been observed with ''bumps'' in their rising light curves shortly after explosion. Here, we present SN 2021qvo: a SN Ia that exhibits a clear early bump in photometry obtained by the Young Supernova Experiment. Photometric and spectroscopic observations of SN 2021qvo show that it has a broader light curve, higher peak luminosity, shallower Si II $λ$5972 pseudo-equivalent width, and lower ejecta velocities than normal SNe Ia, which are all consistent with the characteristics of the 2003fg-like (often called ''super-Chandrasekhar") SN subtype. Including SN 2021qvo, just four known 2003fg-like SNe Ia have sufficient pre-peak data to reveal a rising light-curve bump, and all four have bump detections. Host-galaxy analysis reveals that SN 2021qvo exploded in a low-mass galaxy ${\rm log}(M_{\ast}/M_{\odot}) = 7.83^{+0.17}_{-0.24}$, also consistent with other members of this class. The current leading early-bump 2003fg-like SN Ia progenitor model involves an interaction between the circumstellar material (CSM) and the SN ejecta. We test the validity of this theory by modeling the early bump and subsequent light-curve evolution of SN 2021qvo with the Modular Open Source Fitter for Transients. We find that the bump can be modeled with a best-fit CSM mass in the range $M_\mathrm{CSM}=3.31-8.51 \times 10^{-3} M_\odot$. SN 2021qvo adds to the small but growing number of 2003fg-like SNe Ia with rising light-curve bumps; as the number of these SNe Ia with CSM estimates continues to grow, population-level inferences about the CSM distribution will be able to constrain the progenitor scenario for these SNe Ia. △ Less

Submitted 28 November, 2025; v1 submitted 18 August, 2025; originally announced August 2025.

Comments: 21 pages, 3 tables, 14 figures. Accepted for Publication in ApJ

A Panchromatic View of Late-time Shock Power in the Type II Supernova 2023ixf

Authors: W. V. Jacobson-Galán, L. Dessart, C. D. Kilpatrick, P. J. Patel, K. Auchettl, S. Tinyanont, R. Margutti, V. V. Dwarkadas, K. A. Bostroem, R. Chornock, R. J. Foley, H. Abunemeh, T. Ahumada, P. Arunachalam, M. J. Bustamante-Rosell, D. A. Coulter, C. Gall, H. Gao, X. Guo, J. Hjorth, M. Kaewmookda, M. M. Kasliwal, R. Kaur, C. Larison, N. LeBaron , et al. (17 additional authors not shown)

Abstract: We present multi-wavelength observations of the type II supernova (SN II) 2023ixf during its first two years of evolution. We combine ground-based optical/NIR spectroscopy with Hubble Space Telescope (HST) far- and near-ultraviolet spectroscopy and James Webb Space Telescope (JWST) near- and mid-infrared photometry and spectroscopy to create spectral energy distributions of SN 2023ixf at +374 and… ▽ More We present multi-wavelength observations of the type II supernova (SN II) 2023ixf during its first two years of evolution. We combine ground-based optical/NIR spectroscopy with Hubble Space Telescope (HST) far- and near-ultraviolet spectroscopy and James Webb Space Telescope (JWST) near- and mid-infrared photometry and spectroscopy to create spectral energy distributions of SN 2023ixf at +374 and +620 days post-explosion, covering a wavelength range of ~0.1-30 $μ$m. The multi-band light curve of SN 2023ixf follows a standard radioactive decay decline rate after the plateau until ~500 days, at which point shock powered emission from ongoing interaction between the SN ejecta and circumstellar material (CSM) begins to dominate. This evolution is temporally consistent with 0.3-10 keV X-ray detections of SN 2023ixf and broad ''boxy'' spectral line emission from reprocessing of shock luminosity in a cold dense shell located between forward and reverse shocks. Using the expected absorbed radioactive decay power and the detected X-ray luminosity, we quantify the total shock powered emission at the +374 and +620 day epochs and find that it can be explained by nearly complete thermalization of the reverse shock luminosity as SN 2023ixf interacts with a continuous, ''wind-like'' CSM with a progenitor mass-loss rate of $\dot M \approx 10^{-4}$ M$_{\odot}$ yr$^{-1}$ ($v_w = 20 \pm 5$ km/s). Additionally, we construct multi-epoch spectral models from the non-LTE radiative transfer code CMFGEN, which contain radioactive decay and shock powers, as well as dust absorption, scattering, and emission. We find that models with shock powers of $L_{sh} = (0.5-1) \times 10^{40}$ erg s$^{-1}$ and $(0.5 - 1) \times 10^{-3}$ M$_{\odot}$ of silicate dust in the cold dense shell and/or inner SN ejecta can effectively reproduce the global properties of the late-time (>300 days) UV-to-IR spectra of SN 2023ixf. △ Less

Submitted 15 October, 2025; v1 submitted 15 August, 2025; originally announced August 2025.

Comments: 23 pages, 11 figures. Accepted for publication in ApJL. Full dataset available on GitHub and Zenodo

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

Eccentric von Zeipel-Lidov-Kozai effects under mildly hierarchical triple systems: Influence of Brown corrections upon orbit flipping

Authors: Hao Gao, Hanlun Lei

Abstract: Mildly hierarchical three-body systems are widespread in the Universe, exemplified by planets in stellar binaries and stars in black-hole binaries. In such systems, Brown Hamiltonian corrections play a crucial role in governing the long-term dynamical evolution. In this work, we extend Brown corrections to include octupole-order coupling terms, thereby formulating a more accurate dynamical model f… ▽ More Mildly hierarchical three-body systems are widespread in the Universe, exemplified by planets in stellar binaries and stars in black-hole binaries. In such systems, Brown Hamiltonian corrections play a crucial role in governing the long-term dynamical evolution. In this work, we extend Brown corrections to include octupole-order coupling terms, thereby formulating a more accurate dynamical model for predicting long-term dynamical behaviors. The utilization of the gauge freedom in canonical transformation shows that the quadrupole-octupole coupling term vanishes and the octupole-octupole coupling term is axisymmetric. Under triple systems with different levels of hierarchies, we systematically investigate the impact of Brown corrections on orbital flipping induced by the eccentric von Zeipel-Lidov-Kozai (ZLK) mechanism. Our analysis reveals that, as the hierarchy of triple systems becomes lower, the asymmetry in the flipping regions becomes more significant. The asymmetric structures are examined in detail using Poincare sections and perturbative techniques, showing that Brown corrections are the key factor responsible for breaking the symmetry of flipping regions. Finally, we extend the classical pendulum approximation to our refined model and demonstrate that its analytical predictions agree remarkably well with those derived from perturbative methods, particularly in the high-eccentricity regime. △ Less

Submitted 25 July, 2025; originally announced July 2025.

Comments: 13 pages, 9 figures, accepted for publication in MNRAS

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. (37 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 23 December, 2025; v1 submitted 19 July, 2025; originally announced July 2025.

Comments: 23 pages, 14 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

Constrain magnetar parameters by taking into account the evolutionary effects of radius and moment of inertia with \emph{Swift}/XRT data

Authors: Lin Lan, He Gao, Shunke Ai, Wen-Jin Xie, Yong Yuan, Long Li, Li-Ping Xin, Jian-Yan Wei

Abstract: A newly born millisecond magnetar has been proposed as one possible central engine of some GRBs with X-ray plateau emission. In this work, we systematically analyzed the Swift/XRT data of long GRBs with plateau emission that were detected before 2023 December, and estimated the physical parameters by considering the $R/I$ evolutionary effects. We found that neglecting the $R/I$ evolutionary effect… ▽ More A newly born millisecond magnetar has been proposed as one possible central engine of some GRBs with X-ray plateau emission. In this work, we systematically analyzed the Swift/XRT data of long GRBs with plateau emission that were detected before 2023 December, and estimated the physical parameters by considering the $R/I$ evolutionary effects. We found that neglecting the $R/I$ evolutionary effects can lead to systematic overestimation or underestimation of magnetar parameters such as $B_p$, $P_0$, and $ε$ from 20\% to 50\%. We also found that some tight correlations, which can be approximately expressed as $ε\propto P_0^{1.57\pm0.22}$, $ε\propto B_p^{0.97\pm0.13}$, $B_p\propto P_0^{1.30\pm0.16}$, $E_{\rm wind}\propto E_{\rm jet,iso}^{0.83\pm0.07}(E_{\rm jet}^{0.76\pm0.06})$, $P_0\propto E_{\rm jet,iso}^{-0.29\pm0.03}(E_{\rm jet}^{-0.26\pm0.02})$, $B_p\propto E_{\rm jet,iso}^{-0.58\pm0.06}(E_{\rm jet}^{-0.55\pm0.05})$, and $ε\propto E_{\rm jet,iso}^{-0.55\pm0.07}(E_{\rm jet}^{-0.52\pm0.06})$ for our selected EoSs. The universal correlations suggest that a nascent magnetar with the faster $P_0$, lower $B_p$, and lower $ε$ are more inclined to power a more energetic GRB jet, and the $ε$ and $P_0$ of newborn magnetar are likely to originate from the magnetically induced distortion and correspond to the equilibrium spin period as a result of interaction between the magnetar and its accretion disk, respectively. Finally, we found that the GW signals from the remnants of those GW-dominated GRBs with redshift measurements cannot reach aLIGO sensitivity threshold, and only two cases (GRBs 150323A and 170607A) can reach ET sensitivity threshold. Future GW observations could not only offer the first smoking gun that a protomagnetar can serve as the central engine of GRBs but also play a crucial role in precisely constraining the neutron star EoS. △ Less

Submitted 2 September, 2025; v1 submitted 15 July, 2025; originally announced July 2025.

Comments: 68 pages, 27 figures, and 14 tables, accepted for publication in ApJS, and matched with the published verison

Massive stars exploding in a He-rich circumstellar medium. XI. Diverse evolution of five Ibn SNe 2020nxt, 2020taz, 2021bbv, 2023utc and 2024aej

Authors: Z. -Y. Wang, A. Pastorello, Y. -Z. Cai, M. Fraser, A. Reguitti, W. -L. Lin, L. Tartaglia, D. Andrew Howell, S. Benetti, E. Cappellaro, Z. -H. Chen, N. Elias-Rosa, J. Farah, A. Fiore, D. Hiramatsu, E. Kankare, Z. -T. Li, P. Lundqvist, P. A. Mazzali, C. McCully, J. Mo, S. Moran, M. Newsome, E. Padilla Gonzalez, C. Pellegrino , et al. (31 additional authors not shown)

Abstract: We present the photometric and spectroscopic analysis of five Type Ibn supernovae (SNe): SN 2020nxt, SN 2020taz, SN 2021bbv, SN 2023utc, and SN 2024aej. These events share key observational features and belong to a family of objects similar to the prototypical Type Ibn SN 2006jc. The SNe exhibit rise times of approximately 10 days and peak absolute magnitudes ranging from $-$16.5 to $-$19 mag. Not… ▽ More We present the photometric and spectroscopic analysis of five Type Ibn supernovae (SNe): SN 2020nxt, SN 2020taz, SN 2021bbv, SN 2023utc, and SN 2024aej. These events share key observational features and belong to a family of objects similar to the prototypical Type Ibn SN 2006jc. The SNe exhibit rise times of approximately 10 days and peak absolute magnitudes ranging from $-$16.5 to $-$19 mag. Notably, SN 2023utc is the faintest Type Ibn supernova discovered to date, with an exceptionally low r-band absolute magnitude of $-16.4$ mag. The pseudo-bolometric light curves peak at $(1-10) \times 10^{42}$ erg s$^{-1}$, with total radiated energies on the order of $(1-10) \times 10^{48}$ erg. Spectroscopically, these SNe display relatively slow spectral evolution; the early spectra are characterised by a hot blue continuum and prominent He I emission lines. Early spectra show blackbody temperatures exceeding $10000~\mathrm{K}$, with a subsequent decline in temperature during later phases. Narrow He I lines, indicative of unshocked circumstellar material (CSM), show velocities of approximately $1000~\mathrm{km~s^{-1}}$. The spectra suggest that the progenitors of these SNe underwent significant mass loss prior to the explosion, resulting in a He-rich CSM. Light curve modelling yields estimates for the ejecta mass ($M_{\rm ej}$) in the range $1-3~M_{\odot}$, with kinetic energies ($E_{\rm Kin}$) of $(0.1-1) \times 10^{50}$ erg. The inferred CSM mass ranges from $0.2$ to $1~M_{\odot}$. These findings are consistent with expectations for core-collapse events arising from relatively massive, envelope-stripped progenitors. △ Less

Submitted 18 June, 2025; originally announced June 2025.

Comments: 54 pages, 53 figures, Accepted for publication in Astronomy & Astrophysics

Journal ref: A&A 700, A156 (2025)

Prospects for Time-Domain and Multi-Messenger Science with eXTP

Authors: Shu-Xu Yi, Wen Zhao, Ren-Xin Xu, Xue-Feng Wu, Giulia Stratta, Simone Dall'Osso, Yan-Jun Xu, Andrea Santangelo, Silvia Zane, Shuang-Nan Zhang, Hua Feng, Huan Yang, Junjie Mao, Junqiang Ge, Lijing Shao, Mi-Xiang Lan, He Gao, Lin Lin, Ning Jiang, Qingwen Wu, Tong Liu, Yun-Wei Yu, Xiang-Yu Wang, Jin Zhang, Dafne Guetta , et al. (53 additional authors not shown)

Abstract: In this new era of time-domain and multi-messenger astronomy, various new transients and new phenomena are constantly being discovered thanks to the rapid advances in observations, which provide the excellent opportunity to study the physics in the extreme environments. The enhanced X-ray Timing and Polarimetry mission (eXTP), planned to be launched in 2030, has several key advantages, including a… ▽ More In this new era of time-domain and multi-messenger astronomy, various new transients and new phenomena are constantly being discovered thanks to the rapid advances in observations, which provide the excellent opportunity to study the physics in the extreme environments. The enhanced X-ray Timing and Polarimetry mission (eXTP), planned to be launched in 2030, has several key advantages, including advanced polarimetry, high sensitivity & large effective area, and wide energy range coverage, which make it a groundbreaking project in high-energy astrophysics. In this article, we briefly introduce the potential time-domain and multi-messenger targets for eXTP, including gravitational-wave (GW) counterparts, gamma-ray bursts (GRBs), magnetars and fast radio bursts (FRBs), tidal disruption events (TDEs), supernovae, high energy neutrinos and TeV active galactic nucleus (AGNs), and so on. We discuss the advantages of future eXTP observations for detecting these sources, their detection capabilities, the abilities to distinguish theoretical models, and their applications in gravity and cosmology. △ Less

Submitted 8 September, 2025; v1 submitted 9 June, 2025; originally announced June 2025.

Comments: accepted for publication in the SCIENCE CHINA Physics, Mechanics & Astronomy

Characterising the Standardisation Properties of Type Ia Supernovae in the z band with Hierarchical Bayesian Modelling

Authors: Erin E. Hayes, Suhail Dhawan, Kaisey S. Mandel, David O. Jones, Ryan J. Foley, Stephen Thorp, Matthew Grayling, Sam M. Ward, Aaron Do, Danial Langeroodi, Nicholas Earl, Kaylee M. de Soto, Gautham Narayan, Katie Auchettl, Thomas de Boer, Kenneth C. Chambers, David A. Coulter, Christa Gall, Hua Gao, Luca Izzo, Chien-Cheng Lin, Eugene A. Magnier, Armin Rest, Qinan Wang

Abstract: Type Ia supernovae (SNe Ia) are standardisable candles: their peak magnitudes can be corrected for correlations between light curve properties and their luminosities to precisely estimate distances. Understanding SN Ia standardisation across wavelength improves methods for correcting SN Ia magnitudes. Using 150 SNe Ia from the Foundation Supernova Survey and Young Supernova Experiment, we present… ▽ More Type Ia supernovae (SNe Ia) are standardisable candles: their peak magnitudes can be corrected for correlations between light curve properties and their luminosities to precisely estimate distances. Understanding SN Ia standardisation across wavelength improves methods for correcting SN Ia magnitudes. Using 150 SNe Ia from the Foundation Supernova Survey and Young Supernova Experiment, we present the first study focusing on SN Ia standardisation properties in the z band. Straddling the optical and near-infrared, SN Ia light in the z band is less sensitive to dust extinction and can be collected alongside the optical on CCDs. Pre-standardisation, SNe Ia exhibit less residual scatter in z-band peak magnitudes than in the g and r bands. SNe Ia peak z-band magnitudes still exhibit a significant dependence on light-curve shape. Post-standardisation, the z-band Hubble diagram has a total scatter of RMS = 0.195 mag. We infer a z-band mass step of $γ_{z} = -0.105 \pm 0.031$ mag, which is consistent within 1$σ$ of that estimated from gri data, assuming Rv = 2.61. When assuming different Rv values for high and low mass host galaxies, the z-band and optical mass steps remain consistent within 1$σ$. Based on current statistical precision, these results suggest dust reddening cannot fully explain the mass step. SNe Ia in the z band exhibit complementary standardisability properties to the optical that can improve distance estimates. Understanding these properties is important for the upcoming Vera Rubin Observatory and Nancy G. Roman Space Telescope, which will probe the rest-frame z band to redshifts 0.1 and 1.8. △ Less

Submitted 4 June, 2025; originally announced June 2025.

Comments: 21 pages, 10 figures; in review at MNRAS

Softness Ratio of SWIFT Gamma-ray Bursts and Relevant Correlations

Authors: Fan Xu, Yong-Feng Huang, Liang Li, Jin-Jun Geng, Xue-Feng Wu, Song-Bo Zhang, Chen Deng, Chen-Ran Hu, Xiao-Fei Dong, Hao-Xuan Gao

Abstract: The properties of X-ray flashes (XRFs) and X-ray rich gamma-ray bursts (XRRs) as compared with classical gamma-ray bursts (C-GRBs) have been widely discussed during the \emph{Swift} era. It has been proposed that XRFs and XRRs are low-energy extensions of the GRB population so that they should follow similar correlations. To further examine this idea, we collect a sample of $303$ GRBs detected by… ▽ More The properties of X-ray flashes (XRFs) and X-ray rich gamma-ray bursts (XRRs) as compared with classical gamma-ray bursts (C-GRBs) have been widely discussed during the \emph{Swift} era. It has been proposed that XRFs and XRRs are low-energy extensions of the GRB population so that they should follow similar correlations. To further examine this idea, we collect a sample of $303$ GRBs detected by \emph{Swift} over the past two decades, all of which have reliable redshifts and spectral parameters. The bursts are classified into XRFs, XRRs, and C-GRBs based on their softness ratio (SR), which is calculated by dividing the $25-50$ keV fluence with the $50-100$ keV fluence. A strong correlation is found among the isotropic energy $E_{\mathrm{iso}}$, peak luminosity $L_{\mathrm{p}}$, and rest frame burst duration $T_{90, \mathrm{rest}}$, i.e., $E_{\mathrm{iso}} \propto L_{\mathrm{p}}^{0.88\pm0.02} T_{90, \mathrm{rest}}^{0.58\pm0.02}$. Additionally, two tight three-parameter correlations involving SR and the rest-frame peak energy $E_{\mathrm{p}}$ are also derived, i.e. $E_{\mathrm{p}} \propto E_{\mathrm{iso}}^{0.20\pm0.02} \mathrm{SR}^{-2.27\pm0.15}$ and $E_{\mathrm{p}} \propto L_{\mathrm{p}}^{0.17\pm0.02} \mathrm{SR}^{-2.33\pm0.14}$. It is interesting to note that XRFs, XRRs, and C-GRBs all follow the above correlations. The implications of these correlations and their potential application in cosmology are discussed. △ Less

Submitted 10 May, 2025; originally announced May 2025.

Comments: 20 pages, 9 figures, 6 tables, ApJ accepted

Final Moments III: Explosion Properties and Progenitor Constraints of CSM-Interacting Type II Supernovae

Authors: W. V. Jacobson-Galán, L. Dessart, K. W. Davis, K. A. Bostroem, C. D. Kilpatrick, R. Margutti, A. V. Filippenko, R. J. Foley, R. Chornock, G. Terreran, D. Hiramatsu, M. Newsome, E. Padilla Gonzalez, C. Pellegrino, D. A. Howell, J. P. Anderson, C. R. Angus, K. Auchettl, T. G. Brink, R. Cartier, D. A. Coulter, T. de Boer, M. R. Drout, N. Earl, K. Ertini , et al. (30 additional authors not shown)

Abstract: We present analysis of the plateau and late-time phase properties of a sample of 39 Type II supernovae (SNe II) that show narrow, transient, high-ionization emission lines (i.e., "IIn-like") in their early-time spectra from interaction with confined, dense circumstellar material (CSM). Originally presented by Jacobson-Galán et al 2024a, this sample also includes multicolor light curves and spectra… ▽ More We present analysis of the plateau and late-time phase properties of a sample of 39 Type II supernovae (SNe II) that show narrow, transient, high-ionization emission lines (i.e., "IIn-like") in their early-time spectra from interaction with confined, dense circumstellar material (CSM). Originally presented by Jacobson-Galán et al 2024a, this sample also includes multicolor light curves and spectra extending to late-time phases of 35 SNe with no evidence for IIn-like features at <2 days after first light. We measure photospheric phase light-curve properties for the distance-corrected sample and find that SNe II with IIn-like features have significantly higher luminosities and decline rates at +50 days than the comparison sample, which could be connected to inflated progenitor radii, lower ejecta mass, and/or persistent CSM interaction. However, we find no statistical evidence that the measured plateau durations and $^{56}$Ni masses of SNe II with and without IIn-like features arise from different distributions. We estimate progenitor zero-age main sequence (ZAMS) masses for all SNe with nebular spectroscopy through spectral model comparisons and find that most objects, both with and without IIn-like features, are consistent with progenitor masses <12.5 M$_{\odot}$. Combining progenitor ZAMS masses with CSM densities inferred from early-time spectra suggests multiple channels for enhanced mass loss in the final years before core collapse such as a convection-driven chromosphere or binary interaction. Finally, we find spectroscopic evidence for ongoing ejecta-CSM interaction at radii $>10^{16}$ cm, consistent with substantial progenitor mass-loss rates of $\sim 10^{-4}$--$10^{-5}$ M$_{\odot}$ yr$^{-1}$ ($v_w < 50$ km/s) in the final centuries to millennia before explosion. △ Less

Submitted 7 May, 2025; originally announced May 2025.

Comments: 30 pages, 20 figures, submitted to ApJ

FRB cosmology with the RM-PRS Luminosity Correlation

Authors: Ran Gao, He Gao, Zhengxiang Li, Yuan-Pei Yang

Abstract: Fast Radio Bursts (FRBs) have emerged as a powerful tool for cosmological studies, particularly through the dispersion measure-redshift ($\mathrm{DM}-z$) relation. This work proposes a novel calibration method for FRBs using the Yang-Li-Zhang (YLZ) empirical relation, which links the rotation measure (RM) of FRBs to the luminosity of their associated persistent radio sources (PRS). We demonstrate… ▽ More Fast Radio Bursts (FRBs) have emerged as a powerful tool for cosmological studies, particularly through the dispersion measure-redshift ($\mathrm{DM}-z$) relation. This work proposes a novel calibration method for FRBs using the Yang-Li-Zhang (YLZ) empirical relation, which links the rotation measure (RM) of FRBs to the luminosity of their associated persistent radio sources (PRS). We demonstrate that this approach provides independent constraints on cosmological parameters, bypassing limitations inherent to traditional $\mathrm{DM}-z$ method. Utilizing the current sample of four YLZ-calibrated FRBs, we derive a Hubble constant measurement of $H_0 = 86.18_{-14.99}^{+18.03}\ \mathrm{km\ s^{-1}\ Mpc^{-1}}$ (68\% CL). Monte Carlo simulations indicate that a future catalog of 400 FRB-PSR systems could reduce the relative uncertainty of $H_0$ to 4.5\%. Combining YLZ-calibrated FRBs with $\mathrm{DM}-z$ sample reveals critical synergies: joint analysis of equalized samples ($N=100$ for both methods) reduces the relative uncertainty of $H_0$ to 2.9\%, mainly because the incorporation of PRS observations substantially mitigates the degeneracy between the parameters such as IGM baryon mass fraction ($f_{\rm IGM}$) and other cosmological parameters inherent to the $\mathrm{DM}-z$ relation. △ Less

Submitted 31 October, 2025; v1 submitted 21 April, 2025; originally announced April 2025.

Comments: 8 pages, 5 figures;

Quasi-thermal Photosphere Emission from Structured Jets of Gamma-Ray Bursts

Authors: Ding-Fang Hu, Jin-Jun Geng, Hao-Xuan Gao, Jing-Zhi Yan, Xue-Feng Wu

Abstract: The prompt emission of gamma-ray bursts (GRBs) is supposed to be released from the relativistic jet launched from the central engine. Apart from the non-thermal nature of the spectra in a majority of GRBs, there is evidence for the presence of quasi-thermal components in the prompt emission of a few GRBs according to observations by Fermi satellite. On the other hand, the GRB jet has been revealed… ▽ More The prompt emission of gamma-ray bursts (GRBs) is supposed to be released from the relativistic jet launched from the central engine. Apart from the non-thermal nature of the spectra in a majority of GRBs, there is evidence for the presence of quasi-thermal components in the prompt emission of a few GRBs according to observations by Fermi satellite. On the other hand, the GRB jet has been revealed as structured in recent research. The theoretical observed spectra of photosphere emissions by an off-axis observer and the dependence of the spectra on the viewing angle under the assumption of structured jets remain unexplored. In this paper, we numerically calculate the instantaneous photosphere spectra by different viewing angles from a structured jet, from which relevant temporal and spectral characteristics are derived. Moreover, we address the necessity of proper treatment of the outflow boundary in the photosphere emission scenario. Furthermore, our calculations suggest that the Einstein Probe and Space-based multi-band astronomical Variable Object Monitor will have the capability to detect the short GRBs similar to GRB 170817A up to a luminosity distance of 200Mpc if the off-axis viewing angle is less than 10 degrees. △ Less

Submitted 21 April, 2025; originally announced April 2025.

Comments: 17 pages,10 figures. Accepted for publication in ApJ

Development of 6-inch 80-170 GHz broadband silicon plated horn antenna arrays for primordial gravitational wave search

Authors: Yuanhang He, Shibo Shu, Yaqiong Li, Xuefeng Lu, Ye Chai, Xiang Li, Zhi Chang, He Gao, Yudong Gu, Xufang Li, Zhengwei Li, Zhouhui Liu, Guofeng Wang, Zhongxue Xin, Daikang Yan, Aimei Zhang, Yifei Zhang, Yongjie Zhang, Wenhua Shi, Juexian Cao, Congzhan Liu

Abstract: Searching for primordial gravitational wave in cosmic microwave background (CMB) polarization signal is one of the key topics in modern cosmology. Cutting-edge CMB telescopes requires thousands of pixels to maximize mapping speed. Using modular design, the telescope focal plane is simplified as several detector modules. Each module has hundreds of pixels including antenna arrays, detector arrays,… ▽ More Searching for primordial gravitational wave in cosmic microwave background (CMB) polarization signal is one of the key topics in modern cosmology. Cutting-edge CMB telescopes requires thousands of pixels to maximize mapping speed. Using modular design, the telescope focal plane is simplified as several detector modules. Each module has hundreds of pixels including antenna arrays, detector arrays, and readout arrays. The antenna arrays, as the beam defining component, determine the overall optical response of the detector module. In this article, we present the developments of 6-inch broadband antenna arrays from 80GHz to 170GHz for the future IHEP focal plane module. The arrays are fabricated from 42 6-inch silicon wafers including 456 antennas, 7% more pixels than usual design. The overall in-band cross polarization is smaller than -20 dB and the in-band beam asymmetry is smaller than 10%, fulfilling the requirements for primordial gravitational wave search. △ Less

Submitted 20 April, 2025; originally announced April 2025.

Comments: 13 pages, 14 figures, to be published in Research in Astronomy and Astrophysics

The EMPI Code for Plasma-Induced Effects on Radio Waves I: Non-Magnetized Media and Applications to Fast Radio Bursts

Authors: Nan Xu, He Gao, Yuan-Pei Yang, Bing Zhang, Wei-Yang Wang, Tian-Cong Wang, Ran Gao

Abstract: Electromagnetic waves undergo modifications as they propagate through plasma. We present EMPI (ElectroMagnetic-wave Plasma Interaction), a three-dimensional numerical framework designed to simulate the interaction between radio signals and cold plasma. With input plasma density profiles, intrinsic radio signals, and the time and frequency resolutions of the telescope, the code synthesizes observed… ▽ More Electromagnetic waves undergo modifications as they propagate through plasma. We present EMPI (ElectroMagnetic-wave Plasma Interaction), a three-dimensional numerical framework designed to simulate the interaction between radio signals and cold plasma. With input plasma density profiles, intrinsic radio signals, and the time and frequency resolutions of the telescope, the code synthesizes observed signals using first-principles calculations. EMPI is capable of modeling a wide range of plasma distributions, spanning analytically described smooth functions (e.g., Gaussian or exponential profiles), statistical models (e.g., turbulent screens), and discrete macroscopic structures like isolated plasma clumps, which are difficult to model both analytically and statistically. Validation tests demonstrate excellent agreement with established plasma propagation effects, such as dispersion, lensing, scintillation, and scattering. This code provides an efficient method for handling both analytical and statistical scenarios, bridging the gap between these descriptions. Thanks to its comprehensive capabilities, EMPI is particularly useful for studying radio sources with cosmological origin, especially pulse-like signals such as Fast Radio Bursts (FRBs). As these signals travel through diverse and complex plasma environments across the universe, their properties are inevitably altered, resulting in observable changes. In this context, EMPI serves as a valuable tool for studying the propagation effects of these sources, helping to advance the understanding of their essence and the intervening plasma environments. △ Less

Submitted 3 June, 2025; v1 submitted 4 April, 2025; originally announced April 2025.

Journal ref: Astrophys. J. 985 (2025) 165

A Large-Scale Search for Photometrically Variable AGNs in Dwarf Galaxies Using the Young Supernova Experiment

Authors: Alexander Messick, Vivienne Baldassare, David O. Jones, K. Decker French, Sandra I. Raimundo, Nicholas Earl, Katie Auchettl, David A. Coulter, Mark E. Huber, Margaret E. Verrico, Thomas de Boer, Kenneth C. Chambers, Hua Gao, Chien-Cheng Lin, Richard J. Wainscoat

Abstract: We conduct an analysis of over 60,000 dwarf galaxies (7<=log(M_*/M_\odot)<=10) in search of photometric variability indicative of active galactic nuclei (AGNs). Using data from the Young Supernova Experiment (YSE), a time domain survey on the Pan-STARRS telescopes, we construct light curves for each galaxy in up to four bands (griz) where available. We select objects with AGN-like variability by f… ▽ More We conduct an analysis of over 60,000 dwarf galaxies (7<=log(M_*/M_\odot)<=10) in search of photometric variability indicative of active galactic nuclei (AGNs). Using data from the Young Supernova Experiment (YSE), a time domain survey on the Pan-STARRS telescopes, we construct light curves for each galaxy in up to four bands (griz) where available. We select objects with AGN-like variability by fitting each light curve to a damped random walk (DRW) model. After quality cuts and removing transient contaminants, we identify 1100 variability-selected AGN candidates (representing 2.4% of the available sample). We analyze their spectra to measure various emission lines and calculate black hole (BH) masses, finding general agreement with previously found mass scaling-relations and nine potential IMBH candidates. Furthermore, we re-analyze the light curves for our candidates to calculate the dampening timescale tau_DRW associated with the DRW and see a similar correlation between this value and the BH mass. Finally, we estimate the active fraction as a function of stellar mass and see evidence that active fraction increases with host mass. △ Less

Submitted 1 April, 2025; originally announced April 2025.

Gamma-ray Burst Empirical Correlation between Peak Luminosity and Peak Energy in The ICMART Model

Authors: Xueying Shao, He Gao

Abstract: Internal-Collision-induced Magnetic Reconnection and Turbulence (ICMART) model is a widely accepted model for explaining how high-magnetization jets produce gamma-ray burst (GRB) prompt emissions. In previous works, we show that this model can produce: 1) light curves with a superposition of fast and slow components; 2) a Band-shaped spectrum whose parameters could follow the typical distrib… ▽ More Internal-Collision-induced Magnetic Reconnection and Turbulence (ICMART) model is a widely accepted model for explaining how high-magnetization jets produce gamma-ray burst (GRB) prompt emissions. In previous works, we show that this model can produce: 1) light curves with a superposition of fast and slow components; 2) a Band-shaped spectrum whose parameters could follow the typical distribution of GRB observations; 3) both ``hard to soft" and ``intensity tracking" patterns of spectral evolution. In this work, through simulations of a large sample with methods established in previous work, we show that the ICMART model can also explain the observed empirical relationships (here we focus on the Yonetoku and Liang relations), as long as the magnetic field strength in the magnetic reconnection radiation region is proportional to the mass of the bulk shell, and inversely proportional to the initial magnetization factor of the bulk shell. Our results suggest that during extreme relativistic magnetic reconnection events, an increase in magnetic field strength leads to more intense dissipation, ultimately resulting in a weaker residual magnetic field. △ Less

Submitted 7 December, 2025; v1 submitted 22 March, 2025; originally announced March 2025.

Journal ref: Monthly Notices of the Royal Astronomical Society, Volume 538, Issue 3, April 2025, Pages 2001-2007

GRB Timing: Decoding the Hidden Slow Jets in GRB 060729

Authors: Jin-Jun Geng, Ding-Fang Hu, Hao-Xuan Gao, Yi-Fang Liang, Yan-Long Hua, Guo-Rui Zhang, Tian-Rui Sun, Bing Li, Yuan-Qi Liu, Fan Xu, Chen Deng, Chen-Ran Hu, Ming Xu, Yong-Feng Huang, Miao-Miao Zhang, Min Fang, Jing-Zhi Yan, Tao An, Xue-Feng Wu

Abstract: Gamma-ray bursts (GRBs) are luminous stellar explosions characterized by the ejection of relativistic jets. This work proposes a novel paradigm to study these GRB jets. By analyzing the timing information of prompt pulses and X-ray flares, in conjunction with the multi-wavelength afterglow observations, we identify three distinct jets in the extraordinary GRB 060729, with initial bulk Lorentz fact… ▽ More Gamma-ray bursts (GRBs) are luminous stellar explosions characterized by the ejection of relativistic jets. This work proposes a novel paradigm to study these GRB jets. By analyzing the timing information of prompt pulses and X-ray flares, in conjunction with the multi-wavelength afterglow observations, we identify three distinct jets in the extraordinary GRB 060729, with initial bulk Lorentz factors ranging from approximately 20 to 80, smaller than typical values of $> 100$. These three jets undergo two successive collisions, producing the observed pair of X-ray flares. Following these interactions, the system evolves into a fast, narrow jet and a slower, hollow jet that continues to propagate in the circumburst medium, evidenced by the notable twin bumps observed in the X-ray and optical afterglow of GRB 060729. Our findings demonstrate that the timing of the early emission enables us to measure the velocities of the GRB jets. The proposed paradigm enhances our understanding of jet dynamics and shock interactions and serves as a powerful tool for probing the physics of the central engine with the expanded sample in the current golden era of GRB research. △ Less

Submitted 23 April, 2025; v1 submitted 22 March, 2025; originally announced March 2025.

Comments: 15 pages, 6 figures, 2 tables, ApJL accepted

Report number: 2025, ApJL, 984, L65

Journal ref: https://iopscience.iop.org/article/10.3847/2041-8213/add00e

Spreading and multi-wavelength emissions of an ultra-narrow relativistic jet from GRB 221009A

Authors: Jin-Jun Geng, Ying-Kang Zhang, Hao-Xuan Gao, Fan Xu, Bing Li, Tian-Rui Sun, Ai-Ling Wang, Zhi-Jun Xu, Yuan-Qi Liu, Jun Yang, Chen-Ran Hu, Lauren Rhodes, Liang Li, Yu Wang, Ye Li, Di Xiao, Jia Ren, Bing Zhang, Tao An, Xue-Feng Wu, Yong-Feng Huang, Zi-Gao Dai

Abstract: The long-term evolution of relativistic jets in gamma-ray bursts (GRBs), particularly from days to months post-burst, remains a fundamental puzzle in astrophysics. Here, we report our very long baseline interferometry observation of the brightest GRB 221009A from 5 to 26 days post-burst. Combined with released data, we uncover a remarkable two-stage evolution of the jet lateral size. The jet size… ▽ More The long-term evolution of relativistic jets in gamma-ray bursts (GRBs), particularly from days to months post-burst, remains a fundamental puzzle in astrophysics. Here, we report our very long baseline interferometry observation of the brightest GRB 221009A from 5 to 26 days post-burst. Combined with released data, we uncover a remarkable two-stage evolution of the jet lateral size. The jet size initially grew slowly but later expanded rapidly, challenging conventional scenarios. The slow-evolving stage provides a robust lower limit on the jet opening angle and direct evidence of jet propagation in the uniform interstellar medium at this period. The synergy analysis of the whole jet size evolution and multi-wavelength emissions uncovers that GRB 221009A harbors an ultra-narrow jet (with a half-opening angle $\simeq$ 0.01-0.03~radian) that propagates through a wind-like medium before encountering the interstellar medium, which finally undergoes lateral spreading after significant deceleration. These findings provide crucial new insights into relativistic jet dynamics and establish GRB 221009A as a unique case study for understanding the complex physics of GRB outflows. △ Less

Submitted 22 March, 2025; originally announced March 2025.

Comments: 30 pages, 13 figures, the two first authors contributed equally; comments welcome!

UNIONS: The Ultraviolet Near-Infrared Optical Northern Survey

Authors: Stephen Gwyn, Alan W. McConnachie, Jean-Charles Cuillandre, Ken C. Chambers, Eugene A. Magnier, Michael J. Hudson, Masamune Oguri, Hisanori Furusawa, Hendrik Hildebrandt, Raymond Carlberg, Sara L. Ellison, Junko Furusawa, Raphaël Gavazzi, Rodrigo Ibata, Yannick Mellier, Ken Osato, H. Aussel, Lucie Baumont, Manuel Bayer, Olivier Boulade, Patrick Côté, David Chemaly, Cail Daley, Pierre-Alain Duc, A. Ellien , et al. (64 additional authors not shown)

Abstract: The Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) is a "collaboration of collaborations" that is using the Canada-France-Hawai'i Telescope, the Pan-STARRS telescopes, and the Subaru Observatory to obtain $ugriz$ images of a core survey region of 6250 deg$^2$ of the northern sky. The $10σ$ point source depth of the data, as measured within a 2-arcsecond diameter aperture, are… ▽ More The Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) is a "collaboration of collaborations" that is using the Canada-France-Hawai'i Telescope, the Pan-STARRS telescopes, and the Subaru Observatory to obtain $ugriz$ images of a core survey region of 6250 deg$^2$ of the northern sky. The $10σ$ point source depth of the data, as measured within a 2-arcsecond diameter aperture, are $[u,g,r,i,z] = [23.7, 24.5, 24.2, 23.8, 23.3]$\ in AB magnitudes. UNIONS is addressing some of the most fundamental questions in astronomy, including the properties of dark matter, the growth of structure in the Universe from the very smallest galaxies to large-scale structure, and the assembly of the Milky Way. It is set to become the major ground-based legacy survey for the northern hemisphere for the next decade and provides an essential northern complement to the static-sky science of the Vera C. Rubin Observatory's Legacy Survey of Space and Time. UNIONS supports the core science mission of the {\it Euclid} space mission by providing the data necessary in the northern hemisphere for the calibration of the wavelength dependence of the {\it Euclid} point-spread function and derivation of photometric redshifts in the North Galactic Cap. This region contains the highest quality sky for {\it Euclid}, with low backgrounds from the zodiacal light, stellar density, extinction, and emission from Galactic cirrus. Here, we describe the UNIONS survey components, science goals, data products, and the current status of the overall program. △ Less

Submitted 17 March, 2025; originally announced March 2025.

Comments: submitted to AJ

A second-scale periodicity in an active repeating fast radio burst source

Authors: Chen Du, Yong-Feng Huang, Jin-Jun Geng, Hao-Xuan Gao, Li Zhang, Chen Deng, Lang Cui, Jie Liao, Peng-Fei Jiang, Liang Zhang, Pei Wang, Chen-Ran Hu, Xiao-Fei Dong, Fan Xu, Liang Li, Ze-Cheng Zou, Abdusattar Kurban

Abstract: Fast radio bursts (FRBs) are fierce radio flashes from the deep sky. Abundant observations have indicated that highly magnetized neutron stars might be involved in these energetic bursts, but the underlying trigger mechanism is still enigmatic. Especially, the widely expected periodicity connected to the spin of the central engine has never been discovered, which leads to further debates on the na… ▽ More Fast radio bursts (FRBs) are fierce radio flashes from the deep sky. Abundant observations have indicated that highly magnetized neutron stars might be involved in these energetic bursts, but the underlying trigger mechanism is still enigmatic. Especially, the widely expected periodicity connected to the spin of the central engine has never been discovered, which leads to further debates on the nature of FRBs. Here we report the first discovery of a $\sim 1.7$ s period in the repeating source of FRB 20201124A. This is an active repeater, from which more than 2800 FRBs have been observed on a total of 49 days. The phase-folding method is adopted to analyze the bursts on each day separately. While no periodical signal is found in all other datasets, a clear periodicity does appear on two specific days, i.e. a period of $1.706015(2)$ s on MJD 59310, and a slightly larger period of $1.707972(1)$ s on MJD 59347. A period derivative of $6.14\times10^{-10}$ s s$^{-1}$ can be derived from these two periods, which further implies a surface magnetic field strength of $1.04\times10^{15}$ G and a spin-down age of $44$ years for the central engine. It is thus concluded that FRB 20201124A should be associated with a young magnetar. △ Less

Submitted 15 March, 2025; originally announced March 2025.

Comments: 28 pages, 9 figures, submitted

Precursor Activity Preceding Interacting Supernovae I: Bridging the Gap with SN 2022mop

Authors: S. J. Brennan, S. Barmentloo, S. Schulze, K. W. Smith, R. Hirai, J. J. Eldridge, M. Fraser, H. F. Stevance, S. J. Smartt, S. Anand, A. Aryan, T. -W. Chen, K. K. Das, A. J. Drake, C. Fransson, A. Gangopadhyay, A. Gkini, W. V. Jacobson-Galán, A. Jerkstrand, J. Johansson, M. Nicholl, G. Pignata, N. Sarin, A. Singh, J. Sollerman , et al. (19 additional authors not shown)

Abstract: Over the past two decades, an increasing number of transients have shown luminous activity at their explosion sites weeks to years before an interacting supernova (SN) is observed. For some objects, this pre-SN activity is typically linked to large-scale mass-loss events preceding core collapse, yet its triggering mechanism and the underlying explosion process remain uncertain. We present SN 2022m… ▽ More Over the past two decades, an increasing number of transients have shown luminous activity at their explosion sites weeks to years before an interacting supernova (SN) is observed. For some objects, this pre-SN activity is typically linked to large-scale mass-loss events preceding core collapse, yet its triggering mechanism and the underlying explosion process remain uncertain. We present SN 2022mop, which was initially observed in August 2022, exhibiting nebular emission, including [O I], Mg I], and [Ca II], resembling the late-time (~200 days post-explosion) spectrum of a stripped-envelope SN (SESN) from a progenitor with M[ZAMS] < 18 Msun. SN 2022mop shows strong (~ 1 mag) repeating undulations in its light curve, suggesting late-time interaction. In mid-2024, the transient re-brightened for several months before a Type IIn SN (r[peak] = -18.2 mag) was observed in December 2024, closely resembling the evolution of SN 2009ip. By triangulating both transients using Pan-STARRS images, we determine that both transients are coincident within approximately 3 parsecs. Given the environment, the chance alignment of two isolated SNe is unlikely. We propose a merger-burst scenario: a compact object formed in 2022, is kicked into an eccentric orbit, interacts with its hydrogen-rich companion over subsequent months, and ultimately merges, triggering a Type IIn SN-like transient. △ Less

Submitted 27 March, 2025; v1 submitted 11 March, 2025; originally announced March 2025.

Comments: Submitted to A&A. 17 pages, 16 figures, and 3 tables. Data will be uploaded to WISeREP upon acceptance

EP240801a/XRF 240801B: An X-ray Flash Detected by the Einstein Probe and Implications of its Multiband Afterglow

Authors: Shuai-Qing Jiang, Dong Xu, Agnes P. C. van Hoof, Wei-Hua Lei, Yuan Liu, Hao Zhou, Yong Chen, Shao-Yu Fu, Jun Yang, Xing Liu, Zi-Pei Zhu, Alexei V. Filippenko, Peter G. Jonker, A. S. Pozanenko, He Gao, Xue-Feng Wu, Bing Zhang, Gavin P Lamb, Massimiliano De Pasquale, Shiho Kobayashi, Franz Erik Bauer, Hui Sun, Giovanna Pugliese, Jie An, Valerio D'Elia , et al. (67 additional authors not shown)

Abstract: We present multiband observations and analysis of EP240801a, a low-energy, extremely soft gamma-ray burst (GRB) discovered on August 1, 2024 by the Einstein Probe (EP) satellite, with a weak contemporaneous signal also detected by Fermi/GBM. Optical spectroscopy of the afterglow, obtained by GTC and Keck, identified the redshift of $z = 1.6734$. EP240801a exhibits a burst duration of 148 s in X-ra… ▽ More We present multiband observations and analysis of EP240801a, a low-energy, extremely soft gamma-ray burst (GRB) discovered on August 1, 2024 by the Einstein Probe (EP) satellite, with a weak contemporaneous signal also detected by Fermi/GBM. Optical spectroscopy of the afterglow, obtained by GTC and Keck, identified the redshift of $z = 1.6734$. EP240801a exhibits a burst duration of 148 s in X-rays and 22.3 s in gamma-rays, with X-rays leading by 80.61 s. Spectral lag analysis indicates the gamma-ray signal arrived 8.3 s earlier than the X-rays. Joint spectral fitting of EP/WXT and Fermi/GBM data yields an isotropic energy $E_{γ,\rm{iso}} = (5.57^{+0.54}_{-0.50})\times 10^{51}\,\rm{erg}$, a peak energy $E_{\rm{peak}} = 14.90^{+7.08}_{-4.71}\,\rm{keV}$, a fluence ratio $\rm S(25-50\,\rm{keV})/S(50-100\,\rm{keV}) = 1.67^{+0.74}_{-0.46}$, classifying EP240801a as an X-ray flash (XRF). The host-galaxy continuum spectrum, inferred using Prospector, was used to correct its contribution for the observed outburst optical data. Unusual early $R$-band behavior and EP/FXT observations suggest multiple components in the afterglow. Three models are considered: two-component jet model, forward-reverse shock model and forward-shock model with energy injection. Both three provide reasonable explanations. The two-component jet model and the energy injection model imply a relatively small initial energy and velocity of the jet in the line of sight, while the forward-reverse shock model remains typical. Under the two-component jet model, EP240801a may resemble GRB 221009A (BOAT) if the bright narrow beam is viewed on-axis. Therefore, EP240801a can be interpreted as an off-beam (narrow) jet or an intrinsically weak GRB jet. Our findings provide crucial clues for uncovering the origin of XRFs. △ Less

Submitted 6 March, 2025; originally announced March 2025.

Comments: 22 pages, 11 figures, submitted to ApJ

SN 2024abfo: a partially stripped SN II from a yellow supergiant

Authors: A. Reguitti, A. Pastorello, S. J. Smartt, G. Valerin, G. Pignata, S. Campana, T. -W. Chen, A. Sankar. K., S. Moran, P. A. Mazzali, J. Duarte, I. Salmaso, J. P. Anderson, C. Ashall, S. Benetti, M. Gromadzki, C. P. Gutierrez, C. Humina, C. Inserra, E. Kankare, T. Kravtsov, T. E. Muller-Bravo, P. J. Pessi, J. Sollerman, D. R. Young , et al. (13 additional authors not shown)

Abstract: We present photometric and spectroscopic data of the type IIb supernova (SN) 2024abfo in NGC 1493 (at 11 Mpc). The ATLAS survey discovered the object just a few hours after the explosion, and observed a fast rise on the first day. Signs of the sharp shock break-out peak and the subsequent cooling phase are observed in the ultraviolet and the bluest optical bands in the first couple of days, while… ▽ More We present photometric and spectroscopic data of the type IIb supernova (SN) 2024abfo in NGC 1493 (at 11 Mpc). The ATLAS survey discovered the object just a few hours after the explosion, and observed a fast rise on the first day. Signs of the sharp shock break-out peak and the subsequent cooling phase are observed in the ultraviolet and the bluest optical bands in the first couple of days, while no peak is visible in the reddest filters. Subsequently, in analogy with normal SNe IIb, the light curve of SN 2024abfo rises again in all bands to the broad peak, with the maximum light reached around one month after the explosion. Its absolute magnitude at peak is $M_r=-16.5\pm0.1$ mag, making it a faint SN IIb. The early spectra are dominated by Balmer lines with broad P-Cygni profiles indicating ejecta velocity of 22,500 km/s. One month after the explosion, the spectra display a transition towards being He-dominated, though the H lines do not completely disappear, supporting the classification of SN 2024abfo as a relatively H-rich SN IIb. We identify the progenitor of SN 2024abfo in archival images of the Hubble Space Telescope, the Dark Energy Survey, and the XMM-Newton space telescope, in multiple optical filters. From its spectral energy distribution, the progenitor is consistent with being a yellow supergiant, having an initial mass of 15 $M_{\odot}$. This detection supports an emerging trend of SN IIb progenitors being more luminous and hotter than SN II ones, and being primaries of massive binaries. Within the SN IIb class, fainter events such as SN 2024abfo tend to have cooler and more expanded progenitors than luminous SNe IIb. △ Less

Submitted 25 April, 2025; v1 submitted 5 March, 2025; originally announced March 2025.

Comments: 9 pages, 9 figures, 4 tables, accepted for publication on A&A

Journal ref: A&A 698, A129 (2025)

Building Machine Learning Challenges for Anomaly Detection in Science

Authors: Elizabeth G. Campolongo, Yuan-Tang Chou, Ekaterina Govorkova, Wahid Bhimji, Wei-Lun Chao, Chris Harris, Shih-Chieh Hsu, Hilmar Lapp, Mark S. Neubauer, Josephine Namayanja, Aneesh Subramanian, Philip Harris, Advaith Anand, David E. Carlyn, Subhankar Ghosh, Christopher Lawrence, Eric Moreno, Ryan Raikman, Jiaman Wu, Ziheng Zhang, Bayu Adhi, Mohammad Ahmadi Gharehtoragh, Saúl Alonso Monsalve, Marta Babicz, Furqan Baig , et al. (125 additional authors not shown)

Abstract: Scientific discoveries are often made by finding a pattern or object that was not predicted by the known rules of science. Oftentimes, these anomalous events or objects that do not conform to the norms are an indication that the rules of science governing the data are incomplete, and something new needs to be present to explain these unexpected outliers. The challenge of finding anomalies can be c… ▽ More Scientific discoveries are often made by finding a pattern or object that was not predicted by the known rules of science. Oftentimes, these anomalous events or objects that do not conform to the norms are an indication that the rules of science governing the data are incomplete, and something new needs to be present to explain these unexpected outliers. The challenge of finding anomalies can be confounding since it requires codifying a complete knowledge of the known scientific behaviors and then projecting these known behaviors on the data to look for deviations. When utilizing machine learning, this presents a particular challenge since we require that the model not only understands scientific data perfectly but also recognizes when the data is inconsistent and out of the scope of its trained behavior. In this paper, we present three datasets aimed at developing machine learning-based anomaly detection for disparate scientific domains covering astrophysics, genomics, and polar science. We present the different datasets along with a scheme to make machine learning challenges around the three datasets findable, accessible, interoperable, and reusable (FAIR). Furthermore, we present an approach that generalizes to future machine learning challenges, enabling the possibility of large, more compute-intensive challenges that can ultimately lead to scientific discovery. △ Less

Submitted 29 March, 2025; v1 submitted 3 March, 2025; originally announced March 2025.

Comments: 17 pages 6 figures to be submitted to Nature Communications

Evidence for an Instability-Induced Binary Merger in the Double-Peaked, Helium-Rich Type IIn Supernova 2023zkd

Authors: A. Gagliano, V. A. Villar, T. Matsumoto, D. O. Jones, C. L. Ransome, A. E. Nugent, D. Hiramatsu, K. Auchettl, D. Tsuna, Y. Dong, S. Gomez, P. D. Aleo, C. Angus, T. de Boer, K. A. Bostroem, K. C. Chambers, D. A. Coulter, K. W. Davis, J. R. Fairlamb, J. Farah, D. Farias, R. J. Foley, C. Gall, H. Gao, E. P. Gonzalez , et al. (20 additional authors not shown)

Abstract: We present ultraviolet to infrared observations of the extraordinary Type IIn supernova 2023zkd (SN 2023zkd). Photometrically, it exhibits persistent and luminous precursor emission spanning $\sim$4 years preceding discovery ($M_r\approx-15$ mag, 1,500~days in the observer frame), followed by a secondary stage of gradual brightening in its final year. Post-discovery, it exhibits two photometric pe… ▽ More We present ultraviolet to infrared observations of the extraordinary Type IIn supernova 2023zkd (SN 2023zkd). Photometrically, it exhibits persistent and luminous precursor emission spanning $\sim$4 years preceding discovery ($M_r\approx-15$ mag, 1,500~days in the observer frame), followed by a secondary stage of gradual brightening in its final year. Post-discovery, it exhibits two photometric peaks of comparable brightness ($M_r\lesssim-18.7$ mag and $M_r\approx-18.4$ mag, respectively) separated by 240 days. Spectroscopically, SN 2023zkd exhibits highly asymmetric and multi-component Balmer and He I profiles that we attribute to ejecta interaction with fast-moving ($1,\!000-2,\!000\;\mathrm{km}\;\mathrm{s}^{-1}$) He-rich polar material and slow-moving ($\sim$$400\;\mathrm{km}\;\mathrm{s}^{-1}$) equatorially-distributed H-rich material. He II features also appear during the second light curve peak and evolve rapidly. Shock-driven models fit to the multi-band photometry suggest that the event is powered by interaction with $\sim$$5-6\;M_{\odot}$ of CSM, with $2-3\;M_{\odot}$ associated with each light curve peak, expelled during mass-loss episodes $\sim$$3-4$ and $\sim$$1-2$ years prior to explosion. The observed precursor emission, combined with the extreme mass-loss rates required to power each light curve peak, favors either super-Eddington accretion onto a black hole or multiple long-lived eruptions from a massive star to luminosities that have not been previously observed. We consider multiple progenitor scenarios for SN 2023zkd, and find that the brightening optical precursor and inferred explosion properties are most consistent with a massive ($M_{\mathrm{ZAMS}}\geq30\;M_{\odot}$) and partially-stripped He star undergoing an instability-induced merger with a black hole companion. △ Less

Submitted 26 February, 2025; originally announced February 2025.

Comments: 50 pages, 20 figures, 4 tables. Submitted to ApJ on 26 Feb 2025. Comments welcome!

New insight into the Rapid Burster by Insight-HXMT

Authors: Y. P. Chen, S. Zhang, S. N. Zhang, L. Ji, L. D. Kong, P. J. Wang, L. Tao, M. Y. Ge, C. Z. Liu, F. J. Lu, J. L. Qu, T. P. Li, Y. P. Xu, X. L. Cao, Y. Chen, Q. C. Bu, C. Cai, Z. Chang, G. Chen, L. Chen, T. X. Chen, W. W. Cui, Y. Y. Du, G. H. Gao, H. Gao , et al. (70 additional authors not shown)

Abstract: We report the timing and spectral analyses upon of the type II X-ray bursts from the Rapid Burster (MXB 1730--335) observed by Insight-HXMT and Swift/XRT. By stacking the long-duration bursts, we find for the first time that the hard X-rays are lagging than the soft X-rays by 3 seconds. However, such a lag is not visible for the short-duration bursts, probably because of the poor statistics. For a… ▽ More We report the timing and spectral analyses upon of the type II X-ray bursts from the Rapid Burster (MXB 1730--335) observed by Insight-HXMT and Swift/XRT. By stacking the long-duration bursts, we find for the first time that the hard X-rays are lagging than the soft X-rays by 3 seconds. However, such a lag is not visible for the short-duration bursts, probably because of the poor statistics. For all bursts the energy spectrum is found to be non-thermal, thanks to the broad band coverage of Insight-HXMT. These findings put new insights into the type-II bursts and require a temporally showing-up corona for possible interpretation. △ Less

Submitted 21 February, 2025; originally announced February 2025.

Journal ref: 2021,ApJ,913,150

The Sliding Flux Ramp Demodulation Algorithm with High Sampling Rate in Microwave SQUID Multiplexer

Authors: Guofu Liao, Congzhan Liu, Zhengwei Li, Daikang Yan, Xiangxiang Ren, Yongjie Zhang, Laiyu Zhang, Yu Xu, Shibo Shu, He Gao, Yifei Zhang, Xuefeng Lu, Xufang Li, He Xu, Di Wu

Abstract: Microwave SQUID Multiplexing (uMUX) is a widely used technique in the low temperature detectors community as it offers high capacity of reading out large scale Transition-Edge Sensor (TES) arrays. In this paper, we propose a Sliding Flux Ramp Demodulation (SFRD) algorithm for uMUX readout system. It can achieve a sampling rate in the order of MHz while maintaining a multiplexing ratio about one th… ▽ More Microwave SQUID Multiplexing (uMUX) is a widely used technique in the low temperature detectors community as it offers high capacity of reading out large scale Transition-Edge Sensor (TES) arrays. In this paper, we propose a Sliding Flux Ramp Demodulation (SFRD) algorithm for uMUX readout system. It can achieve a sampling rate in the order of MHz while maintaining a multiplexing ratio about one thousand. Advancing of this large array readout technique makes it possible to observe scientiffc objects with improved time resolution and event count rate. This will be highly helpful for TES calorimeters in X-ray applications, such as X-ray astrophysics missions. △ Less

Submitted 18 February, 2025; originally announced February 2025.

Comments: 12 pages, 5 figures, published on Experimental Astronomy

Photometric Objects Around Cosmic Webs (PAC) Delineated in a Spectroscopic Survey. VIII. Revisiting the Lensing is Low Effect

Authors: Xiaolin Luo, Kun Xu, Yipeng Jing, Hongyu Gao, Hekun Li, Donghai Zhao, Jiaxin Han, Chengliang Wei, Yu Luo

Abstract: The issue of over-predicting the galaxy-galaxy lensing (GGL) signal using conventional galaxy-halo connection models has become well-known as the ``Lensing is Low'' problem, which has been extensively investigated using the Baryon Oscillation Spectroscopic Survey (BOSS) galaxy samples. This issue is also tightly related to the so-called $S_8$ tension. By applying our Photometric objects Around Cos… ▽ More The issue of over-predicting the galaxy-galaxy lensing (GGL) signal using conventional galaxy-halo connection models has become well-known as the ``Lensing is Low'' problem, which has been extensively investigated using the Baryon Oscillation Spectroscopic Survey (BOSS) galaxy samples. This issue is also tightly related to the so-called $S_8$ tension. By applying our Photometric objects Around Cosmic webs (PAC) method to the BOSS survey and the DESI deep photometric survey, we obtained hundreds of cross-correlation measurements to establish an accurate galaxy-halo connection for BOSS galaxies through the halo abundance matching technique (Paper IV). With this galaxy-halo connection, we show in this work that the predicted GGL signals for BOSS galaxies both in the Planck and WMAP Universes actually agree very well with the GGL measurements. We find the best-fitting value $S_8 = 0.8294 \pm 0.0110$, $0.8073 \pm 0.0372$ and $0.8189 \pm 0.0440$ for the CMASS samples with the source galaxies from HSC, DES and KiDS image surveys, respectively. Our work indicates that accurate modeling of the lens population is so critical to interpret the GGL observation. For the scale of $r_p < 0.6\,h^{-1}\rm{Mpc}$, our GGL prediction for LOWZ samples are also in good agreement with the observations of HSC and DES. However, the GGL observation of KiDS is much lower on the small scale. Our results indicate that no significant baryon feedback is needed to suppress the small scale clustering unless the the GGL observation of KiDS on the small scale will be confirmed. △ Less

Submitted 13 February, 2025; originally announced February 2025.

Comments: 13 pages, 8 figures

Performance Analysis of Digital Flux-locked Loop Circuit with Different SQUID $V$-$φ$ Transfer Curves for TES Readout System

Authors: Nan Li, Xiang-xiang Ren, Le-peng Li, Meng-jie Song, Hao-yu Li, Shi-bo Shu, Ya-qiong Li, Yong-jie Zhang, Xu-fang Li, Yu-dong Gu, Cong-zhan Liu, Hai-feng Li, He Gao, Zheng-wei Li

Abstract: A superconducting quantum interference device (SQUID), functioning as a nonlinear response device, typically requires the incorporation of a flux-locked loop (FLL) circuit to facilitate linear amplification of the current signal transmitted through a superconducting transition-edge sensor (TES) across a large dynamic range. This work presents a reasonable model of the SQUID-FLL readout system, bas… ▽ More A superconducting quantum interference device (SQUID), functioning as a nonlinear response device, typically requires the incorporation of a flux-locked loop (FLL) circuit to facilitate linear amplification of the current signal transmitted through a superconducting transition-edge sensor (TES) across a large dynamic range. This work presents a reasonable model of the SQUID-FLL readout system, based on a digital proportional-integral-differential (PID) flux negative feedback algorithm. This work investigates the effect of $V$-$φ$ shape on the performance of digital FLL circuits. Such as the impact factors of bandwidth, design limits of slew rate of the system and the influence of the shapes of SQUID $V$-$φ$ curve. Furthermore, the dynamic response of the system to X-ray pulse signals with rise time ranging from $4.4{\sim}281$ $\mathrm{μs}$ and amplitudes ranging from $6{\sim}8$ $\mathrm{φ_0}$ was simulated. All the simulation results were found to be consistent with the existing mature theories, thereby validating the accuracy of the model. The results also provide a reliable modelling reference for the design of digital PID flux negative feedback and multiplexing SQUID readout electronic systems. △ Less

Submitted 6 February, 2025; originally announced February 2025.

Comments: 9 pages, 11 figures

Characterization of Multiple Channels Room Temperature Readout Electronics for Large Transition-Edge Sensor Array

Authors: N. Li, X. Ren, H. Gao, Z. Zhang, Y. Zhang, C. Liu, H. Li, Z. Li

Abstract: Transition-edge sensor (TES) is a highly sensitive device that is capable of detecting extremely low levels of energy. It is characterised by low noise performance and high energy resolution. A mature method for reading out TES signal is through time-division multiplexing (TDM) direct current superconducting quantum interference device (SQUID). In a TDM system, the signal readout chain represents… ▽ More Transition-edge sensor (TES) is a highly sensitive device that is capable of detecting extremely low levels of energy. It is characterised by low noise performance and high energy resolution. A mature method for reading out TES signal is through time-division multiplexing (TDM) direct current superconducting quantum interference device (SQUID). In a TDM system, the signal readout chain represents a significant source of noise other than the TES intrinsic noise. The noise generated by TES is in the range of several tens to several hundreds of $pA/\sqrt{Hz}$. In order to ensure the high energy resolution of TES, it is necessary to ensure that the noise contribution from the room temperature readout electronics is less than $10$ $pA/\sqrt{Hz}$ above 100 $Hz$. In this work, we have designed a low-noise, high-resolution room temperature readout circuit for TDM. The equivalent current noise contribution of ADC is about $0.05$ $pA/\sqrt{Hz}$ above 100 $Hz$ and $0.46$ $pA\sqrt{Hz}$ under 30:1 multiplexing. The resolution of the analog to digital converter (ADC) is larger than 11.5 bits, which can reconstruct the TES signal without distortion. The readout board, which has eight channels, has JESD204B serial ports, which has greatly simplified the space of room temperature electronics. The readout chain is based on multi-threaded CPU processing and can transfer data at 2 $Gbps$ for each channel in real time. This readout board can be used in a TDM system with smaller size for large TES arrays. △ Less

Submitted 8 February, 2025; v1 submitted 10 January, 2025; originally announced January 2025.

Comments: 9 pages, 6 figures, 2 tables

Science objectives of the Einstein Probe mission

Authors: Weimin Yuan, Lixin Dai, Hua Feng, Chichuan Jin, Peter Jonker, Erik Kuulkers, Yuan Liu, Kirpal Nandra, Paul O'Brien, Luigi Piro, Arne Rau, Nanda Rea, Jeremy Sanders, Lian Tao, Junfeng Wang, Xuefeng Wu, Bing Zhang, Shuangnan Zhang, Shunke Ai, Johannes Buchner, Esra Bulbul, Hechao Chen, Minghua Chen, Yong Chen, Yu-Peng Chen , et al. (71 additional authors not shown)

Abstract: The Einstein Probe (EP) is an interdisciplinary mission of time-domain and X-ray astronomy. Equipped with a wide-field lobster-eye X-ray focusing imager, EP will discover cosmic X-ray transients and monitor the X-ray variability of known sources in 0.5-4 keV, at a combination of detecting sensitivity and cadence that is not accessible to the previous and current wide-field monitoring missions. EP… ▽ More The Einstein Probe (EP) is an interdisciplinary mission of time-domain and X-ray astronomy. Equipped with a wide-field lobster-eye X-ray focusing imager, EP will discover cosmic X-ray transients and monitor the X-ray variability of known sources in 0.5-4 keV, at a combination of detecting sensitivity and cadence that is not accessible to the previous and current wide-field monitoring missions. EP can perform quick characterisation of transients or outbursts with a Wolter-I X-ray telescope onboard. In this paper, the science objectives of the Einstein Probe mission are presented. EP is expected to enlarge the sample of previously known or predicted but rare types of transients with a wide range of timescales. Among them, fast extragalactic transients will be surveyed systematically in soft X-rays, which include γ-ray bursts and their variants, supernova shock breakouts, and the predicted X-ray transients associated with binary neutron star mergers. EP will detect X-ray tidal disruption events and outbursts from active galactic nuclei, possibly at an early phase of the flares for some. EP will monitor the variability and outbursts of X-rays from white dwarfs, neutron stars and black holes in our and neighbouring galaxies at flux levels fainter than those detectable by the current instruments, and is expected to discover new objects. A large sample of stellar X-ray flares will also be detected and characterised. In the era of multi-messenger astronomy, EP has the potential of detecting the possible X-ray counterparts of gravitational wave events, neutrino sources, and ultra-high energy γ-ray and cosmic ray sources. EP is expected to help advance the studies of extreme objects/phenomena and their underlying physical processes revealed in the dynamic X-ray universe, as well as studies in other areas of X-ray astronomy. △ Less

Submitted 13 January, 2025; originally announced January 2025.

Comments: 67 pages, 24 figures, accepted for publication in SCIENCE CHINA Physics, Mechanics & Astronomy

BASSET: Bandpass-Adaptive Single-pulse SEarch Toolkit -- Optimized Sub-Band Pulse Search Strategies for Faint Narrow-Band FRBs

Authors: J. -H. Cao, P. Wang, D. Li, Q. -H. Pan, K. Mao, C. -H. Niu, Y. -K. Zhang, Q. -Y. Qu, W. -J. Lu, J. -S. Zhang, Y. -H. Zhu, Y. -D. Wang, H. -X. Chen, X. -L. Chen, E. Gügercinoğlu, J. -H. Fang, Y. Feng, H. Gao, Y. -F. Huang, J. Li, C. -C. Miao, C. -W. Tsai, J. -M. Yao, S. -P. You, R. -S. Zhao , et al. (7 additional authors not shown)

Abstract: The existing single-pulse search algorithms for fast radio bursts (FRBs) do not adequately consider the frequency bandpass pattern of the pulse, rendering them incomplete for the relatively narrow-spectrum detection of pulses. We present a new search algorithm for narrow-band pulses to update the existing standard pipeline, Bandpass-Adaptive Single-pulse SEarch Toolkit (BASSET). The BASSET employs… ▽ More The existing single-pulse search algorithms for fast radio bursts (FRBs) do not adequately consider the frequency bandpass pattern of the pulse, rendering them incomplete for the relatively narrow-spectrum detection of pulses. We present a new search algorithm for narrow-band pulses to update the existing standard pipeline, Bandpass-Adaptive Single-pulse SEarch Toolkit (BASSET). The BASSET employs a time-frequency correlation analysis to identify and remove the noise involved by the zero-detection frequency band, thereby enhancing the signal-to-noise ratio (SNR) of the pulses. The BASSET algorithm was implemented on the FAST real dataset of FRB 20190520B, resulting in the discovery of additional 79 pulses through reprocessing. The new detection doubles the number of pulses compared to the previously known 75 pulses, bringing the total number of pulses to 154. In conjunction with the pulse calibration and the Markov Chain Monte Carlo (MCMC) simulated injection experiments, this work updates the quantified parameter space of the detection rate. Moreover, a parallel-accelerated version of the BASSET code was provided and evaluated through simulation. BASSET has the capacity of enhancing the detection sensitivity and the SNR of the narrow-band pulses from the existing pipeline, offering high performance and flexible applicability. BASSET not only enhances the completeness of the low-energy narrow-band pulse detection in a more robust mode, but also has the potential to further elucidate the FRB luminosity function at a wider energy scale. △ Less

Submitted 10 January, 2025; originally announced January 2025.

Comments: 22 pages, 11 figures, submitted to ApJS

Photometric Objects Around Cosmic Webs (PAC). VII. Disentangling Mass and Environment Quenching with the Aid of Galaxy-halo Connection in Simulations

Authors: Yun Zheng, Kun Xu, Donghai Zhao, Y. P. Jing, Hongyu Gao, Xiaolin Luo, Ming Li

Abstract: Star formation quenching in galaxies is a critical process in galaxy formation. It is widely believed that the quenching process is dominated by the mass of galaxies and/or their environment. In Paper V, we addressed the challenge to disentangle the effects of mass and environment by employing the PAC method, which combines spectroscopic and deep photometric surveys. This approach enabled us to me… ▽ More Star formation quenching in galaxies is a critical process in galaxy formation. It is widely believed that the quenching process is dominated by the mass of galaxies and/or their environment. In Paper V, we addressed the challenge to disentangle the effects of mass and environment by employing the PAC method, which combines spectroscopic and deep photometric surveys. This approach enabled us to measure the excess surface density of blue and red galaxies around massive central galaxies down to $10^{9.0}M_{\odot}$. However, it is not straightforward to completely separate the two effects. To address this issue, in this paper, we derive the average quenched fraction of central (isolated) galaxies, $\bar{f}_{\mathrm{q}}^{\mathrm{cen}}(M_{*})$, by combining the 3D quenched fraction distribution $f^{\mathrm{sat}}_{\mathrm{q}}(r; M_{*,\mathrm{cen}}, M_{*,\mathrm{sat}})$, reconstructed from the $\bar{n}_2w_{\mathrm{p}}(r_{\mathrm{p}})$ measurements, with the stellar mass-halo mass relation in N-body simulations from Paper IV, and the observed total quenched fraction, $\bar{f}_{\mathrm{q}}^{\mathrm{all}}(M_{*})$. Using $f^{\mathrm{sat}}_{\mathrm{q}}(r;M_{*,\mathrm{cen}},M_{*,\mathrm{sat}})$, $\bar{f}_{\mathrm{q}}^{\mathrm{cen}}(M_{*})$, and the galaxy-halo connection, we assign a quenched probability to each (sub)halo in the simulation, enabling a comprehensive study of galaxy quenching. We find that the mass-quenched fraction increases from 0.3 to 0.87 across the stellar mass range $[10^{9.5}, 10^{11.0}]M_{\odot}$, while the environmental quenched fraction decreases from 0.17 to 0.03. The mass effect dominates galaxy quenching across the entire stellar mass range we studied. Moreover, more massive host halos are more effective at quenching their satellite galaxies, while satellite stellar mass has minimal influence on environmental quenching. △ Less

Submitted 20 March, 2025; v1 submitted 1 January, 2025; originally announced January 2025.

Comments: Accepted to ApJ. Abstract abridged for arxiv. Comments welcome!