Showing 1–50 of 410 results for author: Liang, E

Probing the Nature of High-Redshift Long GRB 250114A and Its Magnetar Central Engine

Authors: Wen-Yuan Yu, Hou-Jun Lü, Xiao Tian, Liang-Jun Chen, En-Wei Liang

Abstract: GRB 250114A is a long-duration gamma-ray burst (GRB) which triggered the Swift/BAT with a spectroscopic high-redshift at $z = 4.732$. The light curve of the prompt emission is composed of three distinct emission episodes, which are separated by quiescent gaps ranging from tens to hundreds of seconds. While the X-ray light curve exhibits the canonical X-ray emission which is composed of several pow… ▽ More GRB 250114A is a long-duration gamma-ray burst (GRB) which triggered the Swift/BAT with a spectroscopic high-redshift at $z = 4.732$. The light curve of the prompt emission is composed of three distinct emission episodes, which are separated by quiescent gaps ranging from tens to hundreds of seconds. While the X-ray light curve exhibits the canonical X-ray emission which is composed of several power-law segments superposition of a giant X-ray flare. More interestingly, there is still significant X-ray emission during the quiescent time in the prompt emission, suggesting a continuously active central engine whose power fluctuates across the $γ$-ray detectability threshold. In this paper, we propose a magnetar as the central engine of GRB 250114A by fitting the X-ray light curve, and infer a magnetic field strength $B_{\rm p}=13.24^{+1.73}_{-5.84} \, \times10^{15}\ \mathrm{G}$ and an initial spin period $P_{0}=14.31^{+0.93}_{-3.16} \, \mathrm{ms}$ of magnetar, with a jet correction, fall within a reasonable range. Furthermore, we also compare the prompt emission, X-ray afterglow, $E_{\mathrm p}$-$E_{γ,\mathrm{iso}}$, and $\varepsilon-$distribution of GBR 250114A with those of other high-$z$ sample-GRBs, and find no significant statistical differences between them. △ Less

Submitted 26 November, 2025; originally announced November 2025.

Comments: 16 pages, 7 figures, and 3 tables. Accepted for publication in ApJ

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

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

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

Submitted 17 November, 2025; originally announced November 2025.

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

Topmetal-L: A Low Noise Charge-Sensitive Pixel Sensor for POLAR2/LPD

Authors: Li-rong Xie, Shi-Qiang Zhou, Di-Fan Yi, Huan-Bo Feng, Zhu-Ke Feng, Dong Wang, Chao-song Gao, En-Wei Liang, Xiang-Ming Sun, Hong-Bang Liu

Abstract: POLAR-2 is a next-generation space astronomy platform led by China, with its core scientific objective focused on high-precision polarization measurements of gamma-ray bursts. As one of its key payloads, the Low-energy Polarization Detector (LPD) is designed to perform wide-field surveys to capture X-ray polarization information from gamma-ray bursts in the 2$\sim$10 keV energy range. This paper p… ▽ More POLAR-2 is a next-generation space astronomy platform led by China, with its core scientific objective focused on high-precision polarization measurements of gamma-ray bursts. As one of its key payloads, the Low-energy Polarization Detector (LPD) is designed to perform wide-field surveys to capture X-ray polarization information from gamma-ray bursts in the 2$\sim$10 keV energy range. This paper presents Topmetal-L, a dedicated charge-sensitive pixel sensor developed for the LPD prototype upgrade. Fabricated in a 130 nm CMOS process in 2024, the chip integrates a 356 $\times$ 512 pixel array with a pixel pitch of 45 $μ$m. Each pixel incorporates a 26 $\times$ 26 $μ$m$^2$ charge-collecting window and is capable of simultaneously outputting both energy and position information of deposited charges. Topmetal-L has been systematically optimized for power consumption, noise performance, and readout efficiency. It exhibits an input dynamic range of 0$\sim$4 ke$^{-}$, a typical charge-to-voltage conversion gain of 76.04 $μ$V/e$^{-}$, an average equivalent noise charge of approximately 22.8 e$^{-}$, a sensitive area exceeding 3.69 cm$^2$, and a total power consumption of 720 mW per chip. To meet the requirements of large-area, high-frame-rate readout for gas-based polarization detectors, a sentinel readout scheme is proposed, reducing the full-frame readout time to 730 $μ$s. A prototype Topmetal-L-based gas polarization detection system was evaluated across key energies: it exhibited a residual modulation of 0.26% $\pm$ 0.45% at 5.90 keV, a modulation factor of 66.67% $\pm$ 0.45% for a linearly polarized 8.05 keV source, and a count rate saturated at 15 k counts$\cdot$cm$^{-2}$$\cdot$s$^{-1}$ when tested at 5.40 keV. △ Less

Submitted 24 November, 2025; v1 submitted 12 November, 2025; originally announced November 2025.

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

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

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

Submitted 29 October, 2025; originally announced October 2025.

Constraint on the Physical Origin of Gamma-Ray Burst Prompt Emission via Its Nondetected Diffuse Neutrino Emission

Authors: Yang-Dong-Jun Ou, Hou-Jun Lü, Jia-Ming Chen, Ben-Yang Zhu, En-Wei Liang

Abstract: The physical origin of prompt emission in gamma-ray bursts (GRBs) remains an open question since it has been studied more than half a century. Three alternative models (i.e. dissipative photosphere, internal shock, and Internal-Collision-induced MAgnetic Reconnection and Turbulence, ICMART) have been proposed to interpret the observations of GRB prompt emission, but none of them can fully interpre… ▽ More The physical origin of prompt emission in gamma-ray bursts (GRBs) remains an open question since it has been studied more than half a century. Three alternative models (i.e. dissipative photosphere, internal shock, and Internal-Collision-induced MAgnetic Reconnection and Turbulence, ICMART) have been proposed to interpret the observations of GRB prompt emission, but none of them can fully interpret all of the observational data collected so far. The question is what is the fraction of these three theoretical models in the prompt emission of GRBs. In this paper, we propose to utilize an innovative method and constrain the fraction of GRB prompt emission models via its nondetected diffuse neutrinos. By adopting two methods (e.g., summing up the individual GRB contributions and assumed luminosity functions of GRB) to calculate diffuse neutrino flux of GRBs for given the benchmark parameters of $Γ=300$ and $\varepsilon_{p} \text{/} \varepsilon_{e}=10$, both approaches indicate that most GRBs should be originated from the ICMART model. Moreover, we find that the fractions of the dissipative photosphere model, the internal shock model, and the ICMART model are constrained to be [0, $0.5\%$], [0, $1.1\%$], and [$98.9\%$, 1], respectively, for the method of summing up the individual GRB contributions. For the method of luminosity functions, the fractions of above three models are constrained to be [0, $6.1\%$], [0, $8.2\%$], and [$91.8\%$, 1], respectively. However, such fractions of different models are also dependent on the parameters of $Γ$ and $\varepsilon_{p} \text{/} \varepsilon_{e}$. △ Less

Submitted 26 November, 2025; v1 submitted 26 October, 2025; originally announced October 2025.

Comments: 9 pages, 4 figures, and 2 tables, matched with the published verison

Journal ref: ApJ,994:91 (2025)

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

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

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

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

Time-Dependent obscuration of a tidal disruption event candidate in the active galactic nucleus CSS100217

Authors: Ying Gu, Xiao Li, Xing-Qian Cheng, Dou-Dou Wang, Xue-Guang Zhang, En-Wei Liang

Abstract: CSS100217 is considered a peculiar tidal disruption event (TDE) candidate occurring in an active galactic nucleus (AGN). Unlike typical TDEs, where the post-flare luminosity is equal to that pre-flare, CSS100217 decayed to $\sim$ 0.4 magnitudes fainter than its pre-flare V band level. In this manuscript, we propose an obscured TDE model to explain the light curve of CSS100217. Assuming that the ti… ▽ More CSS100217 is considered a peculiar tidal disruption event (TDE) candidate occurring in an active galactic nucleus (AGN). Unlike typical TDEs, where the post-flare luminosity is equal to that pre-flare, CSS100217 decayed to $\sim$ 0.4 magnitudes fainter than its pre-flare V band level. In this manuscript, we propose an obscured TDE model to explain the light curve of CSS100217. Assuming that the time-dependent obscuration, caused by the TDE unbound stellar debris, or by nuclear clouds moving around the supermassive black hole (SMBH), follows a Weibull distribution, we find that the light curve of CSS100217 can be described by the tidal disruption of a $4.6_{-0.9}^{+0.9}{\rm M_\odot}$ main-sequence star by a $3.3_{-0.3}^{+0.3}\times10^7{\rm M_\odot}$ black hole. The total energy of the event derived from our fit is $7.23\times10^{53}$ ergs and about 1.38 ${\rm M_\odot}$ of debris mass is accreted by the central SMBH. The model indicates that the contribution of the host galaxy to the observed pre-flare optical luminosity is not-significant compared to that of the AGN, which is consistent with the results of the spectral analysis. These results suggest that obscuration may play an important role in explaining the unusual TDE-like variability observed in CSS100217. △ Less

Submitted 30 September, 2025; originally announced September 2025.

Comments: 6 pages, 5 figures. Accepted by A&A Letter

FRB 20200428 and potentially associated hard X-ray bursts: Maser emission and synchrotron radiation of electrons in a weakly magnetized plasma?

Authors: Xiao Li, En-Wei Liang

Abstract: The temporal and spatial coincidence between FRB 20200428 and hard peaks of the X-ray burst from SGR 1935+2154 suggests their potential association. We attributed them to the plasma synchrotron maser emission and synchrotron radiation of electrons in weakly magnetized, relativistically moving plasma blobs, and Monte Carlo simulation analysis shows that our model can predict observable fast radio b… ▽ More The temporal and spatial coincidence between FRB 20200428 and hard peaks of the X-ray burst from SGR 1935+2154 suggests their potential association. We attributed them to the plasma synchrotron maser emission and synchrotron radiation of electrons in weakly magnetized, relativistically moving plasma blobs, and Monte Carlo simulation analysis shows that our model can predict observable fast radio burst outbursts and associated hard X-ray bursts with current telescopes. We constrained the properties of the blobs, including the Lorentz factor $Γ=5-30$, the magnetization factor $σ=6\times10^{-5}\sim 2\times 10^{-4}$, the electron Lorentz factor $γ_{\rm e,s}=(1.8-3.3)\times10^4$, and the plasma frequency $ν_P=2.48 -42.61$ MHz. The inferred size of the blobs is $\sim 10^{9-10}$ cm, and it is located $\sim 10^{12-14}$ cm from the central engine. By adopting fine-tuned parameter sets, the observed spectra of both the FRB 20200428 outbursts and X-ray bursts can be well represented. The peak flux density ($F_{\rmν_{ pk}}$) of plasma maser emission is sensitive to $σ$ and $ν_P$. Variation in $F_{\rm ν_{pk}}$ can be more than 10 orders of magnitude, while the flux density of the synchrotron emission only varies by $1-2$ orders of magnitude. This can account for the observed sub-energetic radio bursts or giant radio pulses from SGR 1935+2154. △ Less

Submitted 26 August, 2025; originally announced August 2025.

Comments: Accepted by A&A

The color evolution of magnetar-powered kilonova emission in merging neutron star-neutron star systems

Authors: Suo-Ning Wang, Hou-Jun Lü, Xiao-Xuan Liu, Jared Rice, Jia Ren, En-Wei Liang

Abstract: The first direct detection of the gravitational wave (GW) event GW170817 and its electromagnetic (EM) counterpart open a new window for studying of multi-messenger astronomy. However, how to identify the remnant of binary neutron star (NS) merger via EM radiation remain an open question. In this paper, we propose a method of color evolution of kilonova emission to identify its progenitors. We assu… ▽ More The first direct detection of the gravitational wave (GW) event GW170817 and its electromagnetic (EM) counterpart open a new window for studying of multi-messenger astronomy. However, how to identify the remnant of binary neutron star (NS) merger via EM radiation remain an open question. In this paper, we propose a method of color evolution of kilonova emission to identify its progenitors. We assume that the energy of the kilonova is contributed from radioactive decay, magnetar spin-down, and pulsar wind nebula (PWN). The color evolution of kilonova emission associated with short GRB is significant when the spectrum is thermal emission, while it tends towards a constant when the spectrum is non-thermal radiation. On the other hand, if the central engine is a black hole (BH) which is promptly generated by the NS-NS merger or NS-BH merger, then the kilonova is powered only by the radioactive decay. There is no color evolution at the beginning before the peak of kilonova emission, but is significantly and rapidly increasing after the peak. On the contrary, if the central engine is a magnetar or stable NS, the kilonova emission is contributed from radioactive decay, magnetar, and PWN. The color evolution after the peak of kilonova emission is complex behavior which depends on the rotational energy and spin-down time-scale of magnetar, and finally tend to a constant in the late state. △ Less

Submitted 21 August, 2025; originally announced August 2025.

Comments: 11 pages and 4 figure. Accepted for publication in MNRAS

Shear Particle Acceleration in Structured Gamma-Ray Burst Jets: III. The Radiation Physics of Bright Prompt Optical Flash

Authors: Zi-Qi Wang, Xiao-Li Huang, En-Wei Liang

Abstract: The radiation physics of bright prompt optical emission of gamma-ray bursts (GRBs) remains a puzzle. Assuming that the GRB ejecta is structured, we investigated this issue by characterizing the ejecta as an ultra-relativistic uniform jet core surrounded by a mild-relativistic cocoon. The mixed jet-cocoon (MJC) region can accelerate particles through the shear acceleration mechanism. Parameterizing… ▽ More The radiation physics of bright prompt optical emission of gamma-ray bursts (GRBs) remains a puzzle. Assuming that the GRB ejecta is structured, we investigated this issue by characterizing the ejecta as an ultra-relativistic uniform jet core surrounded by a mild-relativistic cocoon. The mixed jet-cocoon (MJC) region can accelerate particles through the shear acceleration mechanism. Parameterizing the radial velocity profile of the MJC region with an exponential function and assuming a uniform magnetic field configuration, we show that the synchrotron radiation of the shear-accelerated electrons can produce a bright optical flash. Emission of the self-synchrotron Compton (SSC) process of the electron population can result in an X-ray excess and an extra MeV-GeV gamma-ray flash relative to the Band function component in the keV-MeV band, which is attributed to the synchrotron radiation of the shock-accelerated electrons in the jet core. Our model reasonably represents the extremely bright optical flash and spectral characteristics of GRBs 990123, 080319B, and 130427A. The inferred magnetic field strength of the MJC region is above $10^{5}$ G, potentially suggesting that the jets of these GRBs are highly magnetized. △ Less

Submitted 8 August, 2025; originally announced August 2025.

Comments: 10 pages, 3 figures, 1 table, Accepted for publication in ApJ

Signature of a magnetar central engine with precession motion in the X-ray emission of GRB 220711B

Authors: Ying-Ze Shan, Xing Yang, Hou-Jun Lü, Jared Rice, Hao-Yu Yuan, Xue-Zhao Chang, Zhao Joseph Zhang, Le Zou, En-Wei Liang

Abstract: The $γ$-ray light curve of long-duration GRB 220711B, is characterized by a multi-peaked structure with a duration lasting $\sim$105 seconds. More interestingly, the X-ray afterglow light curve is composed of a plateau emission smoothly connected with a $\sim t^{-2}$ segment overlapping some flares followed by an extremely steep decay. By analysing the light curves of both prompt emission and X-ra… ▽ More The $γ$-ray light curve of long-duration GRB 220711B, is characterized by a multi-peaked structure with a duration lasting $\sim$105 seconds. More interestingly, the X-ray afterglow light curve is composed of a plateau emission smoothly connected with a $\sim t^{-2}$ segment overlapping some flares followed by an extremely steep decay. By analysing the light curves of both prompt emission and X-ray afterglow, no high-confidence-level quasi-periodic oscillation (QPO) signals are found in the light curves of the prompt emission (e.g., BAT and GBM), but it is found that a QPO signal at $\sim$ 50 s above 6$σ$ confidence level indeed exist in the X-ray afterglow. Here, we propose that a supra-massive magnetar as the central engine of GRB 220711B with precession motion is a good interpretation of the features of the X-ray emission. The initial plateau emission and followed decay segment, as well as the extremely steep-decay segment, are consistent with the physical process of supra-massive magnetar spin-down and then collapse into black hole. Moreover, the QPO signal in the X-ray emission can be explained as an effect of the precession motion of the magnetar. If this is the case, one can derive various magnetar parameters such as the initial period ($P_{\rm{0}}$) and surface magnetic field strength ($B_{\rm{p}}$) within a pseudo-redshift range of [1.08, 4.27]. By considering beaming corrections with jet opening angle $5^{\circ}$, we find that $P_{\rm{0}}$ and $B_{\rm{p}}$ lie within the range of [1.87, 6.25] ms and [$1.47\times 10^{16}$, $3.09\times 10^{16}$] G, respectively. The parameter of $B_{\rm{p}}$ is slightly larger than that of other typical long-duration GRBs, but $P_{\rm{0}}$ fall in a reasonable range. △ Less

Submitted 31 July, 2025; originally announced August 2025.

Comments: 14 pages, 7 figures, and 2 Tables, Accepted for publication in MNRAS

Image of a time-dependent rotating regular black hole

Authors: Sen Guo, En-Wei Liang, Yu-Xiang Huang, Yu Liang, Qing-Quan Jiang, Kai Lin, Li-Fang Li

Abstract: In this study, we develop a modeling framework based on spatio-temporal generalized random fields to simulate the time-evolving accretion flows and their associated imaging signatures around rotating regular black holes. We extend the Matérn field formalism to the spatio-temporal domain and introduce a locally anisotropic tensor structure \(Λ(\mathbf{x})\), which encodes direction-dependent correl… ▽ More In this study, we develop a modeling framework based on spatio-temporal generalized random fields to simulate the time-evolving accretion flows and their associated imaging signatures around rotating regular black holes. We extend the Matérn field formalism to the spatio-temporal domain and introduce a locally anisotropic tensor structure \(Λ(\mathbf{x})\), which encodes direction-dependent correlation scales motivated by Keplerian velocity fields, thereby generating physically informed perturbation structures. Coupled with a computationally efficient light ray-tracing scheme, this framework produces a sequence of time-resolved images of regular black hole shadow and accretion structures. By incorporating light-travel time effects, we identify significant temporal smearing of features within strongly lensed regions and rapidly varying sources, thus enhancing the physical realism of the modeling. Comparison with existing general relativistic magnetohydrodynamic simulations demonstrates that our stochastic generative model maintains statistical consistency while offering substantial computational efficiency. Moreover, the simulated results reproduce the dynamic positional shift of the bright ring structure observed in M87$^{*}$, providing theoretical support for interpreting its time-variable images. △ Less

Submitted 29 July, 2025; originally announced July 2025.

Comments: 26 pages, 17 figures

Journal ref: published Sci.China Phys.Mech.Astron (2025)

A $6.37\,{\rm Hz}$ quasi-periodic oscillating photospheric emission in GRB~240825A

Authors: Guo-Yu Li, Da-Bin Lin, Zhi-Lin Chen, Bao-Quan Huang, Tong Liu, En-Wei Liang

Abstract: Using data from Swift-BAT and Fermi-GBM, we report the first detection of a high-confidence quasi-periodic oscillation (QPO) in the thermal emission of gamma-ray burst GRB~240825A. The spectral analysis of the burst reveals two radiation components, including a thermal emission dominant in $100 \text{--} 300\,\mathrm{keV}$ and a non-thermal emission spanning a wide energy range. During the interva… ▽ More Using data from Swift-BAT and Fermi-GBM, we report the first detection of a high-confidence quasi-periodic oscillation (QPO) in the thermal emission of gamma-ray burst GRB~240825A. The spectral analysis of the burst reveals two radiation components, including a thermal emission dominant in $100 \text{--} 300\,\mathrm{keV}$ and a non-thermal emission spanning a wide energy range. During the interval $2.07 \text{--} 3.25\,\mathrm{s}$ post-trigger, a strong QPO signal at $6.37\,\mathrm{Hz}$ ($\gtrsim 5σ$ confidence) is identified in the $100 \text{--} 300\,\mathrm{keV}$ thermal-dominated band. The variability analysis of the non-thermal component ($15 \text{--} 30\,\mathrm{keV}$) uncovered a $0.67\,\mathrm{Hz}$ QPO, consistent with light-curve modeling using periodic fast-rise exponential decay pulses. The strong QPO in the photospheric emission directly indicates a quasi-periodic oscillating jet. Together with the non-thermal emission variability, we show that this QPO can be explained in terms of a helical structure in the jet, where the viewing angle to the dominant emission region in the jet undergoes periodic changes. △ Less

Submitted 22 July, 2025; originally announced July 2025.

Comments: 37 pages, 14 figures, 6 tables

Radiation Spectrum of the Photospheric Emission for a Turbulent Relativistic Jet

Authors: Guo-Yu Li, Da-Bin Lin, Zhi-Lin Chen, En-Wei Liang

Abstract: The prompt $γ$-rays of gamma-ray bursts (GRBs) may originate from the photosphere of a relativistic jet. However, only a few GRBs have been observed with evident blackbody-like emission, for example, GRB~090902B. It has been demonstrated that internal dissipation processes, such as magnetic reconnection, can occur within the relativistic jet and thereby drive violent turbulence in the dissipation… ▽ More The prompt $γ$-rays of gamma-ray bursts (GRBs) may originate from the photosphere of a relativistic jet. However, only a few GRBs have been observed with evident blackbody-like emission, for example, GRB~090902B. It has been demonstrated that internal dissipation processes, such as magnetic reconnection, can occur within the relativistic jet and thereby drive violent turbulence in the dissipation region. In this paper, we study the photospheric emission of a jet with turbulence below its photosphere. Here, the turbulence is modeled phenomenological under the assumption that the four-velocity of its eddies follows a Gaussian distribution in the jet's co-moving frame. It is found that the turbulence scatters photons to high energies and thus intensifies the emission in the high-energy regime. The corresponding distortion of the radiation field can be preserved if and only if the turbulence occurs in a region with incomplete photon-electron coupling. Consequently, the observed radiation spectrum can be reshaped into a Band-like spectrum. △ Less

Submitted 21 July, 2025; originally announced July 2025.

Comments: 10 pages, 8 figures, accepted for publication in ApJ

Neutron Star-White Dwarf Merger as One Possible Optional Source of Kilonova-like Emission: Implications for GRB 211211A

Authors: Xiao-Xuan Liu, Hou-Jun Lü, Qiu-Hong Chen, Zhao-Wei Du, En-Wei Liang

Abstract: Long-duration GRB 211211A, which lacked an associated supernova at such a low redshift $z=0.076$, but was associated with a possible kilonova emission, has attracted great attention. The neutron star-white dwarf (NS-WD) merger is proposed as a possible progenitor of GRB 211211A, and it could naturally explain the long duration of the prompt emission. However, the NS-WD merger is not an ideal site… ▽ More Long-duration GRB 211211A, which lacked an associated supernova at such a low redshift $z=0.076$, but was associated with a possible kilonova emission, has attracted great attention. The neutron star-white dwarf (NS-WD) merger is proposed as a possible progenitor of GRB 211211A, and it could naturally explain the long duration of the prompt emission. However, the NS-WD merger is not an ideal site for producing heavy elements via r-process nucleosynthesis. In this Letter, we investigate the heavy elements produced in NS-WD mergers based on numerical simulations of nucleosynthesis via SkyNet, and then calculate the resulting kilonova-like emission to compare with the solidly observed case of possible kilonova emission associated with GRB 211211A. By adopting three models (i.e., Model-A, Model-B, and Model-C) from \cite{2023ApJ...956...71K} at different temperatures ($T=4$ GK, 5 GK, and 6 GK), which are treated as free parameters, we find that the mass number of the heaviest element produced in our simulations is less than 90 ($A< 90$). Moreover, by comparing the calculated kilonova-like emission with the afterglow-subtracted observations of the possible kilonova associated with GRB 211211A, it is found that the merger of NS and WD cannot be ruled out as the origin of GRB 211211A to produce the possible kilonova emission if the remnant of the WD-NS merger is a supramassive or stable magnetar. Otherwise, it is difficult to explain the early possible kilonova emission following GRB 211211A by invoking the merger of a WD and an NS. △ Less

Submitted 24 July, 2025; v1 submitted 6 July, 2025; originally announced July 2025.

Comments: 11 pages, 3 figures,and 1 Table, accepted for publication in ApJL,and matched with the published verison

Journal ref: ApJL, 988:L46, 2025

GRB 240825A: Early Reverse Shock and Its Physical Implications

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

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

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

Comments: 31 pages, 9 Figures, 10 Tables

The radiative subpulse modulation and spectral features of PSR B1929$+$10 with the whole pulse phase emission

Authors: Zhengli Wang, Jiguang Lu, Weiyang Wang, Shunshun Cao, Jinchen Jiang, Jiangwei Xu, Kejia Lee, Enwei Liang, Hongguang Wang, Renxin Xu

Abstract: In this work, we observe the nearby pulsar, PSR B1929$+$10, using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We find, for the first time, two new emission components with an extremely weak observed flux density of about $10^{-4}$ of the magnitude of the peak radio emission of PSR B1929$+$10. Our results show that the intrinsic radio emission of PSR B1929$+$10 covers the… ▽ More In this work, we observe the nearby pulsar, PSR B1929$+$10, using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We find, for the first time, two new emission components with an extremely weak observed flux density of about $10^{-4}$ of the magnitude of the peak radio emission of PSR B1929$+$10. Our results show that the intrinsic radio emission of PSR B1929$+$10 covers the $360^{\circ}$ of longitude, demonstrating that this pulsar is a whole $360^{\circ}$ of longitude emission pulsar. We find at least 15 components of pulse emission in the average pulse profile. Additionally, we identify 5 modes of subpulse modulation in different emission regions, which differ from the pulse components. Moreover, the narrowband emission feature and the frequent jumps in the observed linear polarization position angle (PPA) are also detected in the single pulse of this pulsar. To understand the magnetosphere of this pulsar, we analyze the observed PPA variations across the whole $360^{\circ}$ of longitude and fit them using the classical rotating vector model (RVM). For the best-fit model, the inclination angle,$α$, and the impact angle, $β$, of this pulsar are $55^{\circ}.56$ and $53^{\circ}.47$, respectively. Using the rotating magnetosphere approximation of the magnetic dipole field, we investigate the three-dimensional pulsar magnetosphere and the sparking pattern on the polar cap surface. Our analysis indicates that the extremely narrow zone of the polar cap, which is associated with a high-altitude magnetospheric region, is responsible for the weak emission window. This pulsar has extremely high-altitude magnetospheric radio emissions. △ Less

Submitted 1 July, 2025; originally announced July 2025.

Comments: 15 pages, 9 figures, accepted for publication in Astronomy & Astrophysics

Jet precession in gamma-ray bursts: The roles of fallback accretion and disk dynamics

Authors: Yun-Peng Li, Da-Bin Lin, Guo-Yu Li, En-Wei Liang

Abstract: The precession phenomenon of the jet in a gamma-ray burst (GRB) is a key probe of the physics of the central engine. Previous studies generally assumed a fixed precession period when analysing the temporal profiles in GRBs; however, the dynamic evolution of the fallback process and accretion disk can significantly affect the precession behaviour. In this work we present a jet precession model that… ▽ More The precession phenomenon of the jet in a gamma-ray burst (GRB) is a key probe of the physics of the central engine. Previous studies generally assumed a fixed precession period when analysing the temporal profiles in GRBs; however, the dynamic evolution of the fallback process and accretion disk can significantly affect the precession behaviour. In this work we present a jet precession model that incorporates the co-evolution of fallback accretion and the central black hole (BH). Our model demonstrates that the jet precession period initially decreases rapidly during the early fallback phase and subsequently increases nearly linearly as the disk evolves. We find that a higher accretion disk viscosity and a slower BH spin lead to longer precession periods and faster precession period growth rates, and that the geometric structure of the precession system modulates the pulse amplitude of the light curve. By fitting the model to observational data of GRBs with multi-pulse structures, we show that jet precession can naturally explain the increasing pulse intervals and broadened pulse widths observed in both long and short GRBs. △ Less

Submitted 27 June, 2025; originally announced June 2025.

Comments: Accepted for publication in A&A

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

All-sky search for individual Primordial Black Hole bursts with LHAASO

Authors: Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, C. M. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, G. H. Chen, H. X. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen, S. H. Chen , et al. (293 additional authors not shown)

Abstract: Primordial Black Holes~(PBHs) are hypothetical black holes with a wide range of masses that formed in the early universe. As a result, they may play an important cosmological role and provide a unique probe of the early universe. A PBH with an initial mass of approximately $10^{15}$~g is expected to explode today in a final burst of Hawking radiation. In this work, we conduct an all-sky search for… ▽ More Primordial Black Holes~(PBHs) are hypothetical black holes with a wide range of masses that formed in the early universe. As a result, they may play an important cosmological role and provide a unique probe of the early universe. A PBH with an initial mass of approximately $10^{15}$~g is expected to explode today in a final burst of Hawking radiation. In this work, we conduct an all-sky search for individual PBH burst events using the data collected from March 2021 to July 2024 by the Water Cherenkov Detector Array of the Large High Altitude Air Shower Observatory (LHAASO). Three PBH burst durations, 10~s, 20~s, and 100~s, are searched, with no significant PBH bursts observed. The upper limit on the local PBH burst rate density is set to be as low as 181~pc$^{-3}$~yr$^{-1}$ at 99$\%$ confidence level, representing the most stringent limit achieved to date. △ Less

Submitted 2 November, 2025; v1 submitted 30 May, 2025; originally announced May 2025.

Comments: 8 pages, 2 figures

First Identification and Precise Spectral Measurement of the Proton Component in the Cosmic-Ray `Knee'

Authors: The LHAASO Collaboration, Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, C. M. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, G. H. Chen, H. X. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen , et al. (292 additional authors not shown)

Abstract: We report the first high-purity identification of cosmic-ray (CR) protons and a precise measurement of their energy spectrum from 0.15 to 12 PeV using the Large High Altitude Air Shower Observatory (LHAASO). Abundant event statistics, combined with the simultaneous detection of electrons/photons, muons, and Cherenkov light in air showers, enable spectroscopic measurements with statistical and syst… ▽ More We report the first high-purity identification of cosmic-ray (CR) protons and a precise measurement of their energy spectrum from 0.15 to 12 PeV using the Large High Altitude Air Shower Observatory (LHAASO). Abundant event statistics, combined with the simultaneous detection of electrons/photons, muons, and Cherenkov light in air showers, enable spectroscopic measurements with statistical and systematic accuracy comparable to satellite data at lower energies. The proton spectrum shows significant hardening relative to low-energy extrapolations, culminating at 3 PeV, followed by sharp softening. This distinct spectral structure - closely aligned with the knee in the all-particle spectrum - points to the emergence of a new CR component at PeV energies, likely linked to the dozens of PeVatrons recently discovered by LHAASO, and offers crucial clues to the origin of Galactic cosmic rays. △ Less

Submitted 20 May, 2025; originally announced May 2025.

Variabilities of Gamma-ray Bursts from the Dynamics of Fallback Material after Tidal Disruption

Authors: Yun-Peng Li, Da-Bin Lin, Guo-Yu Li, Zi-Min Zhou, En-Wei Liang

Abstract: The gamma-ray burst (GRB) GRB 211211A and GRB 060614, believed to originate from the merger of compact objects, exhibit similarities to the jetted tidal disruption event (TDE) Sw J1644+57, by showing violent variabilities in the light-curve during the decay phase. Previous studies suggest that such fluctuations in TDE may arise from the fallback of tidal disrupted debris. In this paper, we introdu… ▽ More The gamma-ray burst (GRB) GRB 211211A and GRB 060614, believed to originate from the merger of compact objects, exhibit similarities to the jetted tidal disruption event (TDE) Sw J1644+57, by showing violent variabilities in the light-curve during the decay phase. Previous studies suggest that such fluctuations in TDE may arise from the fallback of tidal disrupted debris. In this paper, we introduce the fluctuations of the mass distribution ${\rm d}M/{\rm d}E$ for the debris ejected during the tidal disruption (with energy $E$) and study their impact on jet power. Turbulence induced by tidal force and the self-gravity of the debris may imprint variabilities in ${\rm d}M/{\rm d}E$ during fallback. We model these fluctuations with a power density spectrum $\propto f_{\rm E}^β$, where $f_{\rm E} = 1/E$ and $β$ is the power-law index. We find that the resulting light curve can preserve the fluctuation characteristics from ${\rm d}M/{\rm d}E$. In addition, the observed fluctuations in the light-curves can be reproduced for a given suitable $β$. Based on the observations, we find that the value of $β$ should be around $-1$. △ Less

Submitted 7 May, 2025; originally announced May 2025.

Comments: Accepted to ApJ

Event Rate Density and Luminosity Function of Newborn-Magnetar-Driven X-Ray Transients from Neutron Star Binary Mergers

Authors: Le Zou, Ji-Gui Cheng, Rui-Chong Hu, Wen-Jin Xie, En-Wei Liang

Abstract: X-ray transients (XTs) driven by newborn magnetars from mergers of neutron star binaries (NSBs) were occasionally detected in the narrow-field {\it Chandra} Deep Field-South survey (CDF-S) and the {\it Swift}/XRT observations of short gamma-ray bursts (sGRBs). Quantifying their event rate density (ERD) and luminosity function (LF) is critical for understanding NSB coalescence and magnetar formatio… ▽ More X-ray transients (XTs) driven by newborn magnetars from mergers of neutron star binaries (NSBs) were occasionally detected in the narrow-field {\it Chandra} Deep Field-South survey (CDF-S) and the {\it Swift}/XRT observations of short gamma-ray bursts (sGRBs). Quantifying their event rate density (ERD) and luminosity function (LF) is critical for understanding NSB coalescence and magnetar formation. Utilizing population synthesis calculations incorporating various equations of state (EoS), we derive a local ERD of $\sim 300\,{\rm Gpc^{-3}\,yr^{-1}}$ and a redshift-dependent ERD profile peaking at $z=1.81$ followed by rapid decline beyond $z \sim 4$. Constructing an XT sample based on CDF-S and {\it Swift} observations, we characterize the LF by a single power-law function at $L \leq 4.75 \times 10^{46}\;{\rm erg\;s^{-1}}$ with a slope of $-1.03$, following by a broken power-law function in which the break luminosity is $L_{\rm b} = 4.38 \times 10^{47}\;{\rm erg\;s^{-1}}$ and the slopes are $-0.28$ and $-1.66$. Based on the ERD and the LF, we estimate that the {\it Einstein Probe} ({\it EP}) detection rate is $\sim 31\;{\rm yr^{-1}}$, adopting a conservative threshold flux of $10^{-9}\;{\rm erg}\;{\rm s^{-1}}$, an luminosity range of $L \in [2\times 10^{44},2\times 10^{49}]\;{\rm erg\;s^{-1}}$, and a correction for jet opening angle of $\sim 16^{\circ}$. This detection rate is consistent with the {\it EP} observations during its first-year operation. It is important to note that our estimation is subject to uncertainties arising from the LF derivation. Future {\it EP} observations of these XT events will be crucial in reducing these uncertainties. △ Less

Submitted 4 May, 2025; originally announced May 2025.

Comments: 16 pages, 6 figures, accepted for publication in ApJ

How to identify the object with mass range of $(2.2-3)M_\odot$ in the merger of compact star systems

Authors: ZhaoWei Du, HouJun Lü, Xiaoxuan Liu, XiLong Fan, EnWei Liang

Abstract: High-frequency gravitational-wave (GW) radiation has been detected by LIGO-Virgo-KAGRA in the merger of compact stars. However, two GW events, GW190814 and GW200210, the mass of one companion object falls into the mass region of $(2.2-3)\rm~M_\odot$, and how to identify such object (e.g., as a low-mass black hole (BH) or a massive neutron star (NS)) remains an open question. In this paper, we prop… ▽ More High-frequency gravitational-wave (GW) radiation has been detected by LIGO-Virgo-KAGRA in the merger of compact stars. However, two GW events, GW190814 and GW200210, the mass of one companion object falls into the mass region of $(2.2-3)\rm~M_\odot$, and how to identify such object (e.g., as a low-mass black hole (BH) or a massive neutron star (NS)) remains an open question. In this paper, we propose a method to identify the mystery compact object (MCO) with the mass region of $(2.2-3)\rm~M_\odot$ in a binary system via the possible electromagnetic (EM) radiations before and after the mergers. A multi-band EM emission can be produced with $L\propto(-t)^{7/4}$ (or $L\propto(-t)^{-5/4}$) during the inspiral phase due to the BH battery (or interaction magnetospheres) mechanism, and a bright (or dark) kilonova emission is powered by radioactive decay with ejecta mass ratio $q>1.7$ (or $q<1.7$) during the post-merge state when MCO is as a low-mass BH (or massive NS) to merger with NS. Moreover, by considering the merger system between MCO and a BH when MCO is a massive NS, we find that it requires the BH with high spin (e.g., $a\sim0.8-0.99$) to make sure the tidal disruption event (TDE) occurred, and a multi-band precursor emission and bright kilonova emission can also be produced during the inspiral phase and post-merge state, respectively. In any case, no matter which mechanism we adopt, such precursor emissions are too weak to be detected by most current telescopes unless the distance is close enough. △ Less

Submitted 10 April, 2025; originally announced April 2025.

Comments: 16 pages, 5 figures,and 1 table, accepted for publication in ApJ

GRB 170519A: Thermal Radiation in an X-ray Flare and Decaying Magnetic Fields for the Early-Time Afterglow

Authors: Zi-Min Zhou, Liang-Jun Chen, Rui-Quan Li, Xiang-Gao Wang, Xing-Ling Li, En-Wei Liang, WeiKang Zheng, Alexei V. Filippenko

Abstract: GRB 170519A was discovered by \emph{Swift}/BAT, and then observed by \emph{Swift}/XRT, \emph{Swift}/UVOT, and ground-based telescopes. We report Lick/KAIT observations of GRB 170519A, and make temporal analysis and spectral joint fits of its multiwavelength light curves. The observations present a relatively complete afterglow structure, including two X-ray flares (Flares I and II), optical onset… ▽ More GRB 170519A was discovered by \emph{Swift}/BAT, and then observed by \emph{Swift}/XRT, \emph{Swift}/UVOT, and ground-based telescopes. We report Lick/KAIT observations of GRB 170519A, and make temporal analysis and spectral joint fits of its multiwavelength light curves. The observations present a relatively complete afterglow structure, including two X-ray flares (Flares I and II), optical onset (Slice 1), normal decay (Slices 2 and 3), and a possible jet break. The spectrum of the bright X-ray flare (Flare II) indicates that a thermal component exists at $t = 190$--240~s. \textbf{The blackbody emits in the photospheric radius $R_{\rm ph}\sim 10^{11}$ cm,} and its temperature ($kT$) decreases with time from \textbf{1.08 to 0.37 keV, its Lorentz factor of blackbody ($Γ_{\rm BB}$) decreases with time from 67.71 to 46.70. The luminosity of the blackbody ($L_{\rm BB}$), $kT$ and $Γ_{\rm BB}$ follow the relations $\bf L_{\rm BB} \propto kT^{2.49\pm 0.03}$ and $Γ_{\rm BB}\propto L_{\rm BB}^{0.27}$ (estimated from \cite{fan2012}).} In the optical light curves, there is an onset bump in the early-time afterglow, rising with an index $α_{O,1} \approx -0.43$ and peaking $\sim1174.9$ s since the BAT trigger. The bump then decays with $\bf α_{O,2} \approx 0.88$ in the normal decay phase, and the X-ray flux decays with a similar index of $\bf α_{X,1} \approx 0.95$. There is no obvious spectral evolution in the normal decay phases, with photon index $\hatΓ = 1.86$ and 1.92 in Slices 2 and 3, respectively. We find that the multiwavelength light curves of the GRB 170519A afterglow can be well fitted by an external shock with time-dependent $ε_B$. In the early afterglow, the value of $ε_B$ decays rapidly from $\bf 4.29\times10^{-2}$ to $\bf 8.23\times10^{-3}$. △ Less

Submitted 3 April, 2025; originally announced April 2025.

Constraining the parameters of heavy dark matter and memory-burdened primordial black holes with DAMPE electron measurements

Authors: Tian-Ci Liu, Ben-Yang Zhu, Yun-Feng Liang, Xiao-Song Hu, En-Wei Liang

Abstract: The DArk Matter Particle Explorer (DAMPE) is a space-based instrument for detecting GeV-TeV cosmic rays and gamma rays. High-energy cosmic rays could be emitted from several dark matter candidates theoretically, such as the heavy dark matter (HDM) and the primordial black holes (PBHs). HDM particles with a mass of $>100\,{\rm TeV}$ could decay into $\gtrsim 10\,{\rm TeV}$ electron/positron pairs.… ▽ More The DArk Matter Particle Explorer (DAMPE) is a space-based instrument for detecting GeV-TeV cosmic rays and gamma rays. High-energy cosmic rays could be emitted from several dark matter candidates theoretically, such as the heavy dark matter (HDM) and the primordial black holes (PBHs). HDM particles with a mass of $>100\,{\rm TeV}$ could decay into $\gtrsim 10\,{\rm TeV}$ electron/positron pairs. PBHs with a mass of $\lesssim 10^{10}\,{\rm g}$ would survive to the present day if the Hawking radiation is significantly suppressed due to the memory burden effect and can also lead to the emission of $\gtrsim 10\,{\rm TeV}$ electrons. In this work, we use the DAMPE electron measurements to obtain the constraints on the decay lifetime $τ$ of HDM and the entropy index $k$ of memory-burdened PBHs at $95 \%$ confidence level. The constraints on the fraction $f_{\rm PBH}$ are also derived with a fixed $k$. Furthermore, the high-energy tail of the DAMPE electron spectrum shows a sign of going upwards, possibly suggesting the presence of an additional component; we discuss if this spectral behavior is real, which parameter space is required for it to be attributed to HDM or PBH. We will show that the required parameters have been constrained by existing limits. △ Less

Submitted 17 March, 2025; originally announced March 2025.

Comments: 8 pages, 7 figures

Picking-up Local GRB Candidates Based on Their Host Galaxies

Authors: J. Wang, Y. Xu, L. J. Chen, C. Wu, L. P. Xin, E. W. Liang, J. Y. Wei

Abstract: Rapid identification of candidates of high-value gamma-ray bursts (GRBs), including both high-$z$ and local events, is crucial for outlining subsequent observational strategy. In this paper, we present a model that enables an on-duty astronomer to rapidly identify candidates of local GRBs prior to spectroscopy, provided that these events have been localized at an arcseconds precision. After taking… ▽ More Rapid identification of candidates of high-value gamma-ray bursts (GRBs), including both high-$z$ and local events, is crucial for outlining subsequent observational strategy. In this paper, we present a model that enables an on-duty astronomer to rapidly identify candidates of local GRBs prior to spectroscopy, provided that these events have been localized at an arcseconds precision. After taking into account the mass distribution of the host galaxies of GRBs, the model calculates the two-dimensional cross-match probabilities between a localized GRB and its surrounding nearby galaxies, and then returns the best match with the highest probability. The model is evaluated not only by the observed GRB sample with redshifts up to $z=4$, but also through the simulated GRB samples. By using the recently published GLADE+ galaxies catalog with a completeness of 95\% up to 500Mpc, along with the NED-LVS catalog, the Precision and Recall of the model are determined to be 0.23-0.33 and 0.75, respectively, at the best performance. A dedicated web service, which will be integrated into the SVOM Science User Support System, has been developed to deploy the model. △ Less

Submitted 9 March, 2025; originally announced March 2025.

Comments: 10 pages, 6 figures, 2 table, accepted by PASP

Signature of strange star as the central engine of GRB 240529A

Authors: Xiao Tian, HouJun Lü, WenJun Tan, ShaoLin Xiong, HaoYu Yuan, WenYuan Yu, ShuQing Zhong, WenLong Zhang, EnWei Liang

Abstract: GRB 240529A is a long-duration gamma-ray burst (GRB) whose light curve of prompt emission is composed of a triple-episode structure, separated by quiescent gaps of tens to hundreds of seconds. More interestingly, its X-ray light curve of afterglow exhibits two-plateau emissions, namely, an internal plateau emission that is smoothly connected with a $\sim t^{-0.1}$ segment and followed by a… ▽ More GRB 240529A is a long-duration gamma-ray burst (GRB) whose light curve of prompt emission is composed of a triple-episode structure, separated by quiescent gaps of tens to hundreds of seconds. More interestingly, its X-ray light curve of afterglow exhibits two-plateau emissions, namely, an internal plateau emission that is smoothly connected with a $\sim t^{-0.1}$ segment and followed by a $\sim t^{-2}$ power-law decay. The three episodes in the prompt emission, together with two plateau emissions in X-ray, are unique in the Swift era. They are very difficult to explain with the standard internal/external shock model by invoking a black hole central engine. However, it could be consistent with the prediction of a supramassive magnetar as the central engine, the physical process of phase transition from magnetar to strange star, as well as the cooling and spin-down of the strange star. In this paper, we propose that the first- and second-episode emissions in the prompt $γ-$ray of GRB 240529A are from the jet emission of a massive star collapsing into a supramassive magnetar and the re-activity of central engine, respectively. Then, the third-episode emission of prompt is attributed to the phase transition from a magnetar to a strange star. Finally, the first- and second-plateau emissions of the X-ray afterglow are powered by the cooling and spin-down of the strange star, respectively. The observational data of each component of GRB 240529A are roughly coincident with the estimations of the above physical picture. △ Less

Submitted 17 February, 2025; originally announced February 2025.

Comments: 15 pages, 4 figures, accepted for publication in ApJ

Repeating fast radio bursts from synchrotron maser radiation in localized plasma blobs: Application to FRB 20121102A

Authors: Xiao Li, Fen Lyu, Hai Ming Zhang, Can-Min Deng, En-Wei Liang

Abstract: The radiation physics of repeating fast radio bursts (FRBs) remains enigmatic. Motivated by the observed narrow-banded emission spectrum and ambiguous fringe pattern of the spectral peak frequency ($ν_{\rm pk}$) distribution of some repeating FRBs, such as FRB 20121102A, we propose that the bursts from repeating FRBs arise from synchrotron maser radiation in localized blobs within weakly magnetize… ▽ More The radiation physics of repeating fast radio bursts (FRBs) remains enigmatic. Motivated by the observed narrow-banded emission spectrum and ambiguous fringe pattern of the spectral peak frequency ($ν_{\rm pk}$) distribution of some repeating FRBs, such as FRB 20121102A, we propose that the bursts from repeating FRBs arise from synchrotron maser radiation in localized blobs within weakly magnetized plasma that relativistically moves toward observers. Assuming the plasma moves toward the observers with a bulk Lorentz factor of $Γ=100$ and the electron distribution in an individual blob is monoenergetic ($γ_{\rm e}\sim300$), our analysis shows that bright and narrow-banded radio bursts with peak flux density $\sim$ 1 ${\rm Jy}$ at peak frequency ($ν_{\rm pk}$) $\sim 3.85$ GHz can be produced by the synchrotron maser emission if the plasma blob has a magnetization factor of $σ\sim10^{-5}$ and a frequency of $ν_{\rm P}\sim 4.5$ MHz. The spectrum of bursts with lower $ν_{\rm pk}$ tends to be narrower. Applying our model to the bursts of FRB 20121102A, the distributions of both the observed $ν_{\rm pk}$ and isotropic energy $E_{\rm iso}$ detected by the Arecibo telescope at the L band and the Green Bank Telescope at the C band are successfully reproduced. We find that the $ν_{\rm P}$ distribution exhibits several peaks, similar to those observed in the $ν_{\rm pk}$ distribution of FRB 20121102A. This implies that the synchrotron maser emission in FRB 20121102A is triggered in different plasma blobs with varying $ν_{\rm P}$, likely due to the inhomogeneity of relativistic electron number density. △ Less

Submitted 16 February, 2025; originally announced February 2025.

Comments: Accepted by A&A

Shear Particle Acceleration in Structured Gamma-Ray Burst Jets: II. Viewing Angle Effect on the Prompt Emission and Application to GRB 170817A

Authors: Zi-Qi Wang, Xiao-Li Huang, En-Wei Liang

Abstract: Multi-messenger observations suggest that the gamma-ray burst on Aug. 17, 2017 (GRB 170817A) resulted from off-axial observations of its structured jet, which consists of a narrow ultra-relativistic jet core surrounded by a wide mild-relativistic cocoon. In a serious paper, we explore the emission of shear-accelerated electrons in the mixed jet-cocoon (MJC) region in a series of papers. This paper… ▽ More Multi-messenger observations suggest that the gamma-ray burst on Aug. 17, 2017 (GRB 170817A) resulted from off-axial observations of its structured jet, which consists of a narrow ultra-relativistic jet core surrounded by a wide mild-relativistic cocoon. In a serious paper, we explore the emission of shear-accelerated electrons in the mixed jet-cocoon (MJC) region in a series of papers. This paper focuses on the viewing angle effect for a structured jet by considering the emission from the shear-accelerated electrons. It is found that the observed synchrotron emission peaks at the Infrared band and the synchrotron self-Compton (SSC) emission peaks at the band of hundreds of keV. They are not sensitive to the viewing angle. In the off-axis observations scenario, the prompt emission spectrum is dominated by the emission of the shear-accelerated electrons. The prompt gamma-ray spectrum of GRB 170817A can be well explained with our model by setting the velocity of the inner edge of the cocoon region as 0.9c, the magnetic field strength as 21 G, the injected initial electron Lorentz factor as $10^3$, and the viewing angle as 0.44 rad. We argue that the joint observations in the Infrared/optical and X-ray bands are critical to verify our model. △ Less

Submitted 16 February, 2025; originally announced February 2025.

Comments: 8 pages, 4 figures. Accepted for publication in ApJ

Broadband $γ$-ray spectrum of supernova remnant Cassiopeia A

Authors: Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, C. M. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, H. X. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen, S. H. Chen, S. Z. Chen , et al. (293 additional authors not shown)

Abstract: The core-collapse supernova remnant (SNR) Cassiopeia A (Cas A) is one of the brightest galactic radio sources with an angular radius of $\sim$ 2.5 $\arcmin$. Although no extension of this source has been detected in the $γ$-ray band, using more than 1000 days of LHAASO data above $\sim 0.8$ TeV, we find that its spectrum is significantly softer than those obtained with Imaging Air Cherenkov Telesc… ▽ More The core-collapse supernova remnant (SNR) Cassiopeia A (Cas A) is one of the brightest galactic radio sources with an angular radius of $\sim$ 2.5 $\arcmin$. Although no extension of this source has been detected in the $γ$-ray band, using more than 1000 days of LHAASO data above $\sim 0.8$ TeV, we find that its spectrum is significantly softer than those obtained with Imaging Air Cherenkov Telescopes (IACTs) and its flux near $\sim 1$ TeV is about two times higher. In combination with analyses of more than 16 years of \textit{Fermi}-LAT data covering $0.1 \, \mathrm{GeV} - 1 \, \mathrm{TeV}$, we find that the spectrum above 30 GeV deviates significantly from a single power-law, and is best described by a smoothly broken power-law with a spectral index of $1.90 \pm 0.15_\mathrm{stat}$ ($3.41 \pm 0.19_\mathrm{stat}$) below (above) a break energy of $0.63 \pm 0.21_\mathrm{stat} \, \mathrm{TeV}$. Given differences in the angular resolution of LHAASO-WCDA and IACTs, TeV $γ$-ray emission detected with LHAASO may have a significant contribution from regions surrounding the SNR illuminated by particles accelerated earlier, which, however, are treated as background by IACTs. Detailed modelling can be used to constrain acceleration processes of TeV particles in the early stage of SNR evolution. △ Less

Submitted 7 February, 2025; originally announced February 2025.

Kilonova Emission from Neutron Star Mergers with Different Equations of State

Authors: Wu-Zimo Qiumu, Meng-Hua Chen, Qiu-Hong Chen, En-Wei Liang

Abstract: Kilonova is an optical-infrared transient powered by the radioactive decay of heavy nuclei from binary neutron star mergers. Its observational characteristics depend on the mass and the nuclide composition of meger ejecta, which are sensitive to the equation of state (EoS) of neutron star. We use astrophysical conditions derived from different EoSs as nucleosynthesis inputs to explore the impact o… ▽ More Kilonova is an optical-infrared transient powered by the radioactive decay of heavy nuclei from binary neutron star mergers. Its observational characteristics depend on the mass and the nuclide composition of meger ejecta, which are sensitive to the equation of state (EoS) of neutron star. We use astrophysical conditions derived from different EoSs as nucleosynthesis inputs to explore the impact of various EoS on the $r$-process nucleosynthesis and the kilonova emission. Our results show that both the abundance patterns of merger ejecta and kilonova light curves are strongly dependent on the neutron star EoSs. Given the mass of two neutron stars, the merger with a softer EoS tends to generate a larger amount of ejected material, and may lead to a brighter kilonova peak luminosity. The relationship between the neutron star EoS and the peak luminosity provides a probe for constraining the properties of EoS in multi-messenger observations of neutron star mergers. △ Less

Submitted 31 January, 2025; originally announced January 2025.

Comments: 9 pages, 6 figures. Accepted for publication in RAA

Discovery of high-frequency quasi-periodic oscillation in short-duration gamma-ray bursts

Authors: Xing Yang, Hou-Jun Lü, Jared Rice, En-Wei Liang

Abstract: Rapidly rotating newborn magnetars, which originate from binary neutron star (NS) mergers and serve as the central engines of short gamma-ray bursts (GRBs), may leave some imprints on their prompt gamma-ray light curves even though they are far from their radiating fireballs. A high-frequency quasi-periodic oscillation (QPO) would be a unique feature for the magnetar central engine, especially a h… ▽ More Rapidly rotating newborn magnetars, which originate from binary neutron star (NS) mergers and serve as the central engines of short gamma-ray bursts (GRBs), may leave some imprints on their prompt gamma-ray light curves even though they are far from their radiating fireballs. A high-frequency quasi-periodic oscillation (QPO) would be a unique feature for the magnetar central engine, especially a hypermassive magnetar. By conducting a systematic analysis of the prompt gamma-ray light curves from 605 short GRBs observed by {\em Fermi}/Gamma-ray Burst Monitor, we have identified such QPO signals in three GRBs (e.g. GRB 120323A, GRB 181222B, and GRB 190606A). The QPOs that peaked at $1258^{+6}_{-6}$ Hz for GRB 120323A, $623^{+4}_{-4}$ Hz for GRB 181222B, and $1410^{+4}_{-5}$ Hz for GRB 190606A are all with a confidence level above 5.2 $σ$. The high-frequency QPO signals of those three short GRBs may be caused by a hypermassive magnetar acting as the central engine in a binary NS merger of a binary NS. △ Less

Submitted 19 February, 2025; v1 submitted 23 January, 2025; originally announced January 2025.

Comments: 11 pages, 1 Table, 7 Figures, accepted for publication in MNRAS, and matched with the published verison

Constraining the Nuclear Equation of State of neutron star via high-frequency quasi-periodic oscillation in short gamma-ray bursts

Authors: Jun-Xiang Huang, Hou-Jun Lü, En-Wei Liang

Abstract: The determination of the equation of state (EOS) of a neutron star (NS) and its maximum mass is very important for understanding the formation and properties of NSs under extreme conditions, but they remain open questions. Short-duration gamma-ray bursts (GRBs) are believed to originate from the merger of binary NSs or giant flares (GFs) of soft gamma repeaters (SGRs). Recently, the high-frequency… ▽ More The determination of the equation of state (EOS) of a neutron star (NS) and its maximum mass is very important for understanding the formation and properties of NSs under extreme conditions, but they remain open questions. Short-duration gamma-ray bursts (GRBs) are believed to originate from the merger of binary NSs or giant flares (GFs) of soft gamma repeaters (SGRs). Recently, the high-frequency quasi-periodic oscillations (QPOs) have been claimed to be identified from two short GRBs (GRB 931101B and GRB 910711). In this paper, we propose that the observed high-frequency QPOs in these two short GRBs result from torsional oscillations in the GFs of SGRs associated with cold NSs, or from radial oscillations of hypermassive NSs as the hot remnants of binary NS mergers, and then to constrain the EOS of NSs. For torsional oscillations, the six selected EOSs (TM1, NL3, APR, SLy4, DDME2, and GM1) of NSs suitable for the zero-temperature condition exhibit significant overlap in mass ranges, suggesting that we cannot constrain the EOS of NSs. For radial oscillations, the six selected EOSs (IUF, TM1, TMA, FSG, BHBLp, and NL3) of NSs suitable for the high-temperature condition cannot be ruled out when redshift is considered. However, it is found that the EOS can only be constrained if the redshift and temperature of the remnant can be measured. △ Less

Submitted 24 February, 2025; v1 submitted 17 January, 2025; originally announced January 2025.

Comments: 16 pages, 2 Tables, 10 Figures, accepted for publication in ApJ, and matched with the published verison

A two-hump spectrum in the prompt emission of GRB 240825A

Authors: Hai-Ming Zhang, Zi-Qi Wang, Cui-Yuan Dai, Yi-Yun Huang, Ruo-Yu Liu, En-Wei Liang, Xiang-Yu Wang

Abstract: An extra hard spectral component that extends to GeV energies, in additional to the typical sub- MeV Band component, appears in several gamma-ray burst (GRBs) detected by Fermi Large Area Telescopes (LAT). Only in one case (i.e., GRB 090926A), a spectral break feature at the high energy end is identified in the extra hard component, but the photon counts are not enough to distinguish between the c… ▽ More An extra hard spectral component that extends to GeV energies, in additional to the typical sub- MeV Band component, appears in several gamma-ray burst (GRBs) detected by Fermi Large Area Telescopes (LAT). Only in one case (i.e., GRB 090926A), a spectral break feature at the high energy end is identified in the extra hard component, but the photon counts are not enough to distinguish between the cutoff model and the broken power law model for the spectral break. In this work, we report the detection of an extra hard component showing the spectral break in GRB 240825A. We find that a broken power-law model fits the spectral data of the extra component better than a single power-law with an exponential cutoff in the time resolved spectrum for the second emission pulse, with a break at about 50 MeV. This spectral feature disfavors the gamma-ray opacity to pair creation as the origin of the spectral break, but points to an intrinsic peak for the extra component. The low ratio between the peak of the extra hard component and that of the Band component challenges the synchrotron self-Compton origin for the extra component. Alternative scenarios, such as the inverse Compton scattering of the photosphere emission, are discussed. In addition, we find a clear transition from the prompt emission to afterglow emission at GeV energies in GRB 240825A, manifested by a temporal steep decay and an unique spectral evolution. △ Less

Submitted 22 April, 2025; v1 submitted 6 January, 2025; originally announced January 2025.

Comments: Accepted for publication in the ApJ Letters

A central tidal disruption event candidate in high redshift quasar SDSS J000118.70+003314.0

Authors: Ying Gu, Xue-Guang Zhang, Xing-Qian Chen, Xing Yang, En-Wei Liang

Abstract: We report a high-redshift ($z=1.404$) tidal disruption event (TDE) candidate in SDSS J000118.70+003314.0 (SDSS J0001), which is a quasar with apparent broad Mg~{\sc ii} emission line. The long-term variability in its nine-year photometric $ugriz$-band light curves, obtained from the SDSS Stripe82 and the PHOTOOBJALL databases, can be described by the conventional TDE model. Our results suggest tha… ▽ More We report a high-redshift ($z=1.404$) tidal disruption event (TDE) candidate in SDSS J000118.70+003314.0 (SDSS J0001), which is a quasar with apparent broad Mg~{\sc ii} emission line. The long-term variability in its nine-year photometric $ugriz$-band light curves, obtained from the SDSS Stripe82 and the PHOTOOBJALL databases, can be described by the conventional TDE model. Our results suggest that the TDE is a main-sequence star with mass of $1.905_{-0.009}^{+0.023}{\rm M_\odot}$ tidally disrupted by a black hole (BH) with mass {$6.5_{-2.6}^{+3.5}\times10^7{\rm M_\odot}$}. The BH mass is about 7.5 times smaller than the virial BH mass derived from the broad Mg~{\sc ii} emission line, which can be explained by non-virial dynamic properties of broad emission lines from TDEs debris. Furthermore, we examine the probability that the event results from intrinsic variability of quasars, which is about $0.009\%$, through applications of the DRW/CAR process. Alternative explanations for the event are also discussed, such as the scenarios of dust obscurations, microlensing and accretion. Our results provide clues to support that TDEs could be detectable in broad line quasars as well as in quiescent galaxies, and to indicate the variability of some active galactic nuclei may be partly attributed to central TDEs. △ Less

Submitted 22 December, 2024; originally announced December 2024.

Comments: 13 pages,12 figures,accepted by MNRAS

Impact of nuclear mass models on $r$-process nucleosynthesis and heavy element abundances in $r$-process enhanced metal-poor stars

Authors: Meng-Hua Chen, Li-Xin Li, En-Wei Liang, Ning Wang

Abstract: Due to the lack of experimental data on extremely neutron-rich nuclei, theoretical values derived from nuclear physics models are essential for the rapid neutron capture process ($r$-process). Metal-poor stars enriched by the $r$-process offer valuable cases for studying the impact of nuclear physics models on $r$-process nucleosynthesis. This study analyzes four widely used nuclear physics models… ▽ More Due to the lack of experimental data on extremely neutron-rich nuclei, theoretical values derived from nuclear physics models are essential for the rapid neutron capture process ($r$-process). Metal-poor stars enriched by the $r$-process offer valuable cases for studying the impact of nuclear physics models on $r$-process nucleosynthesis. This study analyzes four widely used nuclear physics models in detail: Finite-Range Droplet Model, Hartree-Fock-Bogoliubov, Duflo-Zuker, and Weizs$\ddot{\rm a}$cker-Skyrme (WS4). Theoretical values predicted by the WS4 model are found to be in good agreement with experimental data, with deviations significantly smaller than those predicted by other models. The heavy element abundances observed in $r$-process enhanced metal-poor stars can be accurately reproduced by $r$-process nucleosynthesis simulations using the WS4 model, particularly for the rare earth elements. This suggests that nuclear data provided by nuclear physics model like WS4 are both essential and crucial for $r$-process nucleosynthesis studies. △ Less

Submitted 25 November, 2024; originally announced November 2024.

Comments: 8 pages, 7 figures, Accepted for publication in A&A

Journal ref: A&A 693, A1 (2025)

Shear Particle Acceleration in Structured Gamma-Ray Burst Jets: I. Physical Origin of the Band Function and Application to GRBs 090926A, 131108A, and 160509A

Authors: Zi-Qi Wang, Xiao-Li Huang, En-Wei Liang

Abstract: The radiation physics of gamma-ray bursts (GRBs) remains an open question. Based on the simulation analysis and recent observations, it was proposed that GRB jets are composed of a narrow ultra-relativistic core surrounded by a wide sub-relativistic cocoon. We show that emission from the synchrotron radiations and the synchrotron self-Compton (SSC) process of shear-accelerated electrons in the mix… ▽ More The radiation physics of gamma-ray bursts (GRBs) remains an open question. Based on the simulation analysis and recent observations, it was proposed that GRB jets are composed of a narrow ultra-relativistic core surrounded by a wide sub-relativistic cocoon. We show that emission from the synchrotron radiations and the synchrotron self-Compton (SSC) process of shear-accelerated electrons in the mixed jet-cocoon (MJC) region and internal-shock-accelerated electrons in the jet core is potentially explained the spectral characteristics of the prompt gamma-rays. Assuming an exponential-decay velocity profile, the shear flow in the MJC region can accelerate electrons up to $γ_{\rm e,\max} \sim 10^4$ for injected electrons with $γ_{\rm e,inject}=3 \times 10^2$, if its magnetic field strength ($B_{\rm cn}$) is $100$ G and its inner-edge velocity ($β_{\rm cn, 0}$) is 0.9c. The cooling of these electrons is dominated by the SSC process, and the emission flux peaks at the keV band. In addition, the energy flux of synchrotron radiations of internal-shock-accelerated electrons ($γ_e=10^{4}\sim 10^{5}$) peaks at around the keV$-$MeV band, assuming a bulk Lorentz factor of 300, a magnetic field strength of $\sim 10^{6}$ G for the jet core. Adding the flux from both the jet core and the MJC region, the total spectral energy distribution (SED) illustrates similar characteristics as the broadband observations of GRBs. The bimodal and Band-Cut spectra observed in GRBs 090926A, 131108A, and 160509A can be well fit with our model. The derived $B_{\rm cn}$ varies from 54 G to 450 G and $β_{\rm cn,0}=0. 83\sim 0.91$c. △ Less

Submitted 17 November, 2024; originally announced November 2024.

Comments: 12 pages, 6 figures. Accepted for publication in ApJ

Kinematics of Young Stellar Objects Under Various Stellar Feedback

Authors: Longhui Yang, Dejian Liu, Chaojie Hao, Zehao Lin, YingJie Li, Yiwei Dong, Zu-Jia Lu, En-Wei Liang, Y. Xu

Abstract: Based on the Gaia Data Release 3 and APOGEE datasets, we investigate the kinematic differences between young stellar objects (YSOs) and their parent clouds in five nearby star-forming regions. Overall, the 1D velocity differences between Class II YSOs and their parent molecular cloud range from [0, 1.4] km/s. In feedback environments dominated by outflows, massive stars, and supernova feedback, th… ▽ More Based on the Gaia Data Release 3 and APOGEE datasets, we investigate the kinematic differences between young stellar objects (YSOs) and their parent clouds in five nearby star-forming regions. Overall, the 1D velocity differences between Class II YSOs and their parent molecular cloud range from [0, 1.4] km/s. In feedback environments dominated by outflows, massive stars, and supernova feedback, the corresponding velocity differences range from [0, 1.4] km/s, [0.1, 0.4] km/s, and [0.1, 1] km/s, respectively. These results indicate that YSO kinematics are not significantly affected by these different types of feedback environment. Additionally, compared to the Class II YSOs, Class III YSOs have slightly larger velocities and dispersions. △ Less

Submitted 14 November, 2024; originally announced November 2024.

Comments: 19 pages, 17 figures, accepted by ApJS

Image of the Kerr-Newman black hole surrounded by a thin accretion disk

Authors: Sen Guo, Yu-Xiang Huang, En-Wei Liang, Yu Liang, Qing-Quan Jiang, Kai Lin

Abstract: The image of a Kerr-Newman (KN) black hole (BH) surrounded by a thin accretion disk is derived. By employing elliptic integrals and ray-tracing methods, we analyze photon trajectories around the KN BH. At low observation inclination angles, the secondary image of particles is embedded within the primary image. However, as the inclination increases, the primary and secondary images separate, formin… ▽ More The image of a Kerr-Newman (KN) black hole (BH) surrounded by a thin accretion disk is derived. By employing elliptic integrals and ray-tracing methods, we analyze photon trajectories around the KN BH. At low observation inclination angles, the secondary image of particles is embedded within the primary image. However, as the inclination increases, the primary and secondary images separate, forming a hat-like structure. The spin and charge of the BH, along with the observer's inclination angle, affect the image's asymmetry and the distortion of the inner shadow. To investigate the redshift distribution on the accretion disk, we extended the inner boundary of the accretion disk to the event horizon. The results show that the redshift distribution is significantly influenced by the observation inclination angle. Furthermore, we conducted a detailed analysis of the KN BH image using fisheye camera ray-tracing techniques and found that the optical appearance and intensity distribution of the BH vary at different observation frequencies (specifically at 230GHz and 86GHz). We also examined differences in intensity distribution for prograde and retrograde accretion disk scenarios. Comparing observational at the two frequencies, we found that both the total intensity and peak intensity at 86GHz are higher than those at 230GHz. △ Less

Submitted 12 November, 2024; originally announced November 2024.

Comments: 26 pages, 21 figures

Journal ref: The Astrophysical Journal, 975:237, 2024

Detection of two TeV gamma-ray outbursts from NGC 1275 by LHAASO

Authors: Zhen Cao, F. Aharonian, Axikegu, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, J. T. Cai, Q. Cao, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, Liang Chen, Lin Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. H. Chen, S. Z. Chen, T. L. Chen , et al. (254 additional authors not shown)

Abstract: The Water Cherenkov Detector Array (WCDA) is one of the components of Large High Altitude Air Shower Observatory (LHAASO) and can monitor any sources over two-thirds of the sky for up to 7 hours per day with >98\% duty cycle. In this work, we report the detection of two outbursts of the Fanaroff-Riley I radio galaxy NGC 1275 that were detected by LHAASO-WCDA between November 2022 and January 2023… ▽ More The Water Cherenkov Detector Array (WCDA) is one of the components of Large High Altitude Air Shower Observatory (LHAASO) and can monitor any sources over two-thirds of the sky for up to 7 hours per day with >98\% duty cycle. In this work, we report the detection of two outbursts of the Fanaroff-Riley I radio galaxy NGC 1275 that were detected by LHAASO-WCDA between November 2022 and January 2023 with statistical significance of 5.2~$σ$ and 8.3~$σ$. The observed spectral energy distribution in the range from 500 GeV to 3 TeV is fitted by a power-law with a best-fit spectral index of $α=-3.37\pm0.52$ and $-3.35\pm0.29$, respectively. The outburst flux above 0.5~TeV was ($4.55\pm 4.21)\times~10^{-11}~\rm cm^{-2}~s^{-1}$ and ($3.45\pm 1.78)\times~10^{-11}~\rm cm^{-2}~s^{-1}$, corresponding to 60\%, 45\% of Crab Nebula flux. Variation analysis reveals the variability time-scale of days at the TeV energy band. A simple test by one-zone synchrotron self-Compton model reproduces the data in the gamma-ray band well. △ Less

Submitted 18 April, 2025; v1 submitted 2 November, 2024; originally announced November 2024.

Comments: 11 pages, 8 figures, 3 tables

An Extreme Radio Fluctuation of Pulsar B1929$+$10

Authors: Zhengli Wang, Shunshun Cao, Jiguang Lu, Yulan Liu, Xun Shi, Jinchen Jiang, Enwei Liang, Weiyang Wang, Heng Xu, Renxin Xu

Abstract: We report the detection of an extreme flux decrease accompanied by clear dispersion measure (DM) and rotation measure (RM) variations for pulsar B1929+10 during the 110-minute radio observation with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The radio flux decreases by 2 to 3 orders of magnitude within a rapid time scale of about 20 minutes. Meanwhile, the variations of DM a… ▽ More We report the detection of an extreme flux decrease accompanied by clear dispersion measure (DM) and rotation measure (RM) variations for pulsar B1929+10 during the 110-minute radio observation with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The radio flux decreases by 2 to 3 orders of magnitude within a rapid time scale of about 20 minutes. Meanwhile, the variations of DM and RM are approximately 0.05 pc cm$^{-3}$ and 0.7 rad m$^{-2}$, respectively. Frequency-dependent analysis of DM indicates an extremely weak chromatic DM feature, which does not notably affect the radiative behavior detected. Moreover, the pulsar timing analysis shows an additional time delay from 100 $μ$s to 400 $μ$s in the event. These results are speculated to be due to the eclipse and bend for the radio emission of pulsar B1929+10 by a highly dense outflow from the pulsar. This not only impacts the intrinsic radio emission feature but also affects the pulsar timing behavior. Nevertheless, a plasma lens effect lasting around 20 minutes could also be responsible for the event. △ Less

Submitted 22 October, 2024; originally announced October 2024.

Comments: 13 pages, 6 figures. Accepted for publication in ApJL

A Comprehensive Analysis of Insight-HXMT Gamma-Ray Burst Data. I. Power Density Spectrum

Authors: Zi-Min Zhou, Xiang-Gao Wang, En-Wei Liang, Jia-Xin Cao, Hui-Ya Liu, Cheng-Kui Li, Bing Li, Da-Bin Lin, Tian-Ci Zheng, Rui-Jing Lu

Abstract: Power Density Spectrum (PDS) is one of the powerful tools to study light curves of gamma-ray bursts (GRBs). We show the average PDS and individual PDS analysis with {\it Hard X-ray Modulation Telescope} (also named \insighthxmt) GRBs data. The values of power-law index of average PDS ($α_{\bar{P}}$) for long GRBs (LGRBs) vary from 1.58-1.29 (for 100-245, 245-600, and 600-2000 keV). The \insighthxm… ▽ More Power Density Spectrum (PDS) is one of the powerful tools to study light curves of gamma-ray bursts (GRBs). We show the average PDS and individual PDS analysis with {\it Hard X-ray Modulation Telescope} (also named \insighthxmt) GRBs data. The values of power-law index of average PDS ($α_{\bar{P}}$) for long GRBs (LGRBs) vary from 1.58-1.29 (for 100-245, 245-600, and 600-2000 keV). The \insighthxmt\ data allow us to extend the energy of the LGRBs up to 2000 keV, and a relation between $α_{\bar{P}}$ and energy $E$, $α_{\bar{P}}\propto E^{-0.09}$ (8-2000 keV) is obtained. We first systematically investigate the average PDS and individual PDS for short GRBs (SGRBs), and obtain $α_{\bar{P}}\propto E^{-0.07}$ (8-1000 keV), where the values of $α_{\bar{P}}$ vary from 1.86 to 1.34. The distribution of power-law index of individual PDS ($α$) of SGRB, is consistent with that of LGRB, and the $α$ value for the dominant timescale group (the bent power-law, BPL) is higher than that for the no-dominant timescale group (the single power-law, PL). Both LGRBs and SGRBs show similar $α$ and $α_{\bar{P}}$, which indicates that they may be the result of similar stochastic processes. The typical value of dominant timescale $τ$ for LGRBs and SGRBs is 1.58 s and 0.02 s, respectively. It seems that the $τ$ in proportion to the duration of GRBs $T_{90}$, with a relation $τ\propto T_{90}^{0.86}$. The GRB light curve may result from superposing a number of pulses with different timescales. No periodic and quasi-periodical signal above the 3$σ$ significance threshold is found in our sample. △ Less

Submitted 17 October, 2024; originally announced October 2024.

Journal ref: 2024, apj, 972, 190.

Neutrino constraints and detection prospects from gamma-ray bursts with different jet compositions

Authors: Yang-Dong-Jun Ou, Hou-Jun Lü, Xue-Zhao Chang, Xiao-Xuan Liu, En-Wei Liang

Abstract: The prompt emission mechanism of gamma-ray bursts (GRBs) is a long-standing open question, and GRBs have been considered as potential sources of high-energy neutrinos. Despite many years of search for the neutrino events associated with GRBs from IceCube, there were no results. However, the absence of search results for neutrinos provides a unique opportunity to constrain the parameter space of GR… ▽ More The prompt emission mechanism of gamma-ray bursts (GRBs) is a long-standing open question, and GRBs have been considered as potential sources of high-energy neutrinos. Despite many years of search for the neutrino events associated with GRBs from IceCube, there were no results. However, the absence of search results for neutrinos provides a unique opportunity to constrain the parameter space of GRB jet models. In this paper, we chose four peculiar GRBs with two different types of jet composition to investigate neutrino emission. It is found that only GRB 211211A could be well constrained within the dissipative photosphere model. By adopting the specific parameters of the photosphere, one can obtain $\varepsilon _{\rm p}/\varepsilon_{\rm e}<8$ for $f_{\rm p}>0.2$ from GRB 211211A. For the Internal-collision-induced Magnetic Reconnection and Turbulence (ICMART) model, we can effectively constrain neither GRB 230307A nor GRB 080916C. Moreover, we also investigate the detection prospects of high-energy neutrinos from GRBs and find that it is difficult to detect at least one high-energy neutrino associated with GRBs from the ICMART model even during the IceCube-Gen2 operation. For the GRB 211211A-like events, it is possible to detect at least one neutrino coincident with the gravitational wave during the IceCube-Gen2 operation, if such an event originated from mergers of compact stars within the photosphere dissipation. △ Less

Submitted 23 November, 2024; v1 submitted 12 October, 2024; originally announced October 2024.

Comments: 15 pages, 10 figures, matched with the published verison

Journal ref: The Astrophysical Journal, 976: 174 (10pp), 2024 December 1

The thermal emission in short GRBs with extended emission observed by Fermi/GBM

Authors: Xue-Zhao Chang, Hou-Jun Lü, Xing Yang, Jia-Ming Chen, En-Wei Liang

Abstract: Short gamma-ray bursts (SGRBs) with extended emission (EE) are composed of initial main emission (ME) with a short-hard spike, followed by a long-lasting EE. Whether the ME and EE originated from the same origin or not, as well as the jet composition, remains an open question. In this paper, we present a systematic analysis of 36 gamma ray bursts (GRBs) in our sample, which are identified as the c… ▽ More Short gamma-ray bursts (SGRBs) with extended emission (EE) are composed of initial main emission (ME) with a short-hard spike, followed by a long-lasting EE. Whether the ME and EE originated from the same origin or not, as well as the jet composition, remains an open question. In this paper, we present a systematic analysis of 36 gamma ray bursts (GRBs) in our sample, which are identified as the category of SGRBs with EE as observed by Fermi/Gamma-ray Burst Monitor. By extracting time-integrated spectra of ME and EE with cutoff power-law or Band models for our sample, we find that 20 out of 36 SGRBs have $α$ values that exceed the death line (e.g., -2/3) of synchrotron emission within either ME or EE phases, and we suggest that the quasi-thermal component should exist in the prompt emission. Then, we extract the time-resolved spectra of our samples, but only four GRBs are bright enough to extract the time-resolved spectra. We find that both thermal and nonthermal emissions do exist in the prompt emission of those four bright GRBs, which suggests that a hybrid jet (e.g., matter and Poynting-flux outflow) in GRBs should exist. Moreover, strong positive correlations (e.g., $F_{\rm tot}-Γ$ and $F_{\rm tot}-kT$) in the time-resolved spectra of ME and EE for those four GRBs have been discovered. This indicates that the spectral evolution of both ME and EE seem to share similar behavior, possibly from the same physical origin. △ Less

Submitted 5 November, 2024; v1 submitted 12 October, 2024; originally announced October 2024.

Comments: 30 pages, 9 figures and 11 tables, matched with the published verison

Journal ref: The Astrophysical Journal Supplement Series, 275: 9 (21pp), 2024 November 5

Comparison between the emission torus and the measured toroidal magnetic field for the Crab and Vela nebula

Authors: Wei Deng, Fei Xie, Kuan Liu, Mingyu Ge, Youli Tuo, Fabio La Monaca, Alessandro Di Marco, En-wei Liang

Abstract: Polarization measurements provide insight into the magnetic field, a critical aspect of the dynamics and emission properties around the compact object. In this paper, we present the polarized magnetic field of the Crab outer torus and the Vela arc utilizing Imaging X-ray Polarimetry Explorer observation data. The polarization angle (PA) measured for the Crab outer torus exhibits two monotonic evol… ▽ More Polarization measurements provide insight into the magnetic field, a critical aspect of the dynamics and emission properties around the compact object. In this paper, we present the polarized magnetic field of the Crab outer torus and the Vela arc utilizing Imaging X-ray Polarimetry Explorer observation data. The polarization angle (PA) measured for the Crab outer torus exhibits two monotonic evolutions along the azimuth angle, which are consistent with the normal line of the elliptical ring. There is a slight increase in PA along the azimuth angle for both the inner arc and the outer arc of the Vela nebula. The polarized magnetic vector along the outer torus of the Crab nebula shows the polarized magnetic field aligns with Crab outer torus structure. The PA variation along the Crab outer torus suggests a bulk flow speed of 0.8c. Meanwhile, the Vela nebula polarized magnetic field does not exactly align with the Vela arc structure. We noted that the Crab nebula possesses a polarized toroidal magnetic field, where as the Vela nebula exhibits an incomplete toroidal magnetic field. △ Less

Submitted 7 October, 2024; originally announced October 2024.

Comments: 8 pages, 5 figures

Origin of TeV Emission in GRB 221009A: Co-effort of the External Reverse and Forward Shocks

Authors: Zhi-Lin Chen, Da-Bin Lin, Guo-Yu Li, En-Wei Liang

Abstract: The TeV emission detected in just five gamma-ray bursts (GRBs) is generally ascribed to the synchrotron emission or the synchrotron self-Compton process in the external forward shock. The brightest gamma-ray burst, GRB 221009A, with an unprecedented detected high energy flux of TeV emission, poses a serious challenge to the above scenario. Different from previous works, we involve the long burstin… ▽ More The TeV emission detected in just five gamma-ray bursts (GRBs) is generally ascribed to the synchrotron emission or the synchrotron self-Compton process in the external forward shock. The brightest gamma-ray burst, GRB 221009A, with an unprecedented detected high energy flux of TeV emission, poses a serious challenge to the above scenario. Different from previous works, we involve the long bursting behavior of GRB~221009A in modeling its external-shocks. The TeV emission together with the later multi-band afterglows of GRB 221009A are all successfully reproduced. It is firstly found that the TeV emission in the early phase is mainly from the co-effort of the external reverse and forward shocks, i.e., the inverse-Compton scattering of the synchrotron emission from the external reverse-shock by the electrons in the external forward-shock. This is owing to that the long bursting behavior leads to a long lasting of energy injection into the external shock and the corresponding reverse-shock. In the later phase, the TeV emission is dominated by the synchrotron self-Compton process in the external forward-shock, which is consistent with previous scenario. Our results indicate the vital role of the external reverse-shock in shaping the early TeV emission of GRBs. △ Less

Submitted 7 October, 2024; originally announced October 2024.

Comments: 9 pages, 4 figures, 2 tables

LHAASO detection of very-high-energy gamma-ray emission surrounding PSR J0248+6021

Authors: Zhen Cao, F. Aharonian, Q. An, Axikegu, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, J. T. Cai, Q. Cao, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, Liang Chen, Lin Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. H. Chen, S. Z. Chen , et al. (255 additional authors not shown)

Abstract: We report the detection of an extended very-high-energy (VHE) gamma-ray source coincident with the location of middle-aged (62.4~\rm kyr) pulsar PSR J0248+6021, by using the LHAASO-WCDA data of live 796 days and LHAASO-KM2A data of live 1216 days. A significant excess of \gray induced showers is observed both by WCDA in energy bands of 1-25~\rm TeV and KM2A in energy bands of $>$ 25~\rm TeV with 7… ▽ More We report the detection of an extended very-high-energy (VHE) gamma-ray source coincident with the location of middle-aged (62.4~\rm kyr) pulsar PSR J0248+6021, by using the LHAASO-WCDA data of live 796 days and LHAASO-KM2A data of live 1216 days. A significant excess of \gray induced showers is observed both by WCDA in energy bands of 1-25~\rm TeV and KM2A in energy bands of $>$ 25~\rm TeV with 7.3 $σ$ and 13.5 $σ$, respectively. The best-fit position derived through WCDA data is R.A. = 42.06$^\circ \pm$ 0.12$^\circ$ and Dec. = 60.24$^\circ \pm $ 0.13$^\circ$ with an extension of 0.69$^\circ\pm$0.15$^\circ$ and that of the KM2A data is R.A.= 42.29$^\circ \pm $ 0.13$^\circ$ and Dec. = 60.38$^\circ \pm$ 0.07$^\circ$ with an extension of 0.37$^\circ\pm$0.07$^\circ$. No clear extended multiwavelength counterpart of this LHAASO source has been found from the radio band to the GeV band. The most plausible explanation of the VHE \gray emission is the inverse Compton process of highly relativistic electrons and positrons injected by the pulsar. These electrons/positrons are hypothesized to be either confined within the pulsar wind nebula or to have already escaped into the interstellar medium, forming a pulsar halo. △ Less

Submitted 3 December, 2024; v1 submitted 6 October, 2024; originally announced October 2024.

Comments: 12 pages, 10 figures, Accepted by Sci. China-Phys. Mech. Astron

Potential Chromospheric Evaporation in A M-dwarf's Flare Triggered by Einstein Probe Mission

Authors: J. Wang, X. Mao, C. Gao, H. Y. Liu, H. L. Li, H. W. Pan, C. Wu, Y. Liu, G. W. Li, L. P. Xin, S. Jin, D. W. Xu, E. W. Liang, W. M. Yuan, J. Y. Wei

Abstract: Although flares from late-type main-sequence stars have been frequently detected in multi-wavelength, the associated dynamical process has been rarely reported so far. Here, we report follow-up observations of an X-ray transient triggered by WXT onboard the Einstein Probe at UT08:45:08 in 2024, May 7. The photometry in multi-bands and time-resolved spectroscopy started at 3 and 7.5 hours after the… ▽ More Although flares from late-type main-sequence stars have been frequently detected in multi-wavelength, the associated dynamical process has been rarely reported so far. Here, we report follow-up observations of an X-ray transient triggered by WXT onboard the Einstein Probe at UT08:45:08 in 2024, May 7. The photometry in multi-bands and time-resolved spectroscopy started at 3 and 7.5 hours after the trigger, respectively, which enables us to identify the transient as a flare of the M-dwarf 2MASS J12184187-0609123. The bolometric energy released in the flare is estimated to be $\sim10^{36}\ \mathrm{erg}$ from its X-ray light curve. The H$α$ emission-line profile obtained at about 7 hours after the trigger shows an evident blue asymmetry with a maximum velocity of $200-250\ \mathrm{km\ s^{-1}}$. The blue wing can be likely explained by the chromospheric temperature (cool) upflow associated with chromospheric evaporation, in which the mass of the evaporating plasma is estimated to be $1.2\times10^{18}$g. In addition, a prominence eruption with an estimated mass of $7\times10^{15}\mathrm{g}<M_{\mathrm{p}}<7\times10^{18}\mathrm{g}$ can not be entirely excluded. △ Less

Submitted 3 October, 2024; originally announced October 2024.

Comments: 13 pages, 5 figures and 3 tables, accepted by AJ