arXiv subjects

Da-Bin Lin

Publications and source records attributed to Da-Bin Lin.

At least 19 recordsLinked to original sources

arXiv2026

Migration Traps as Variability Attractors. II. Nonmonotonic X-Ray Timing Signatures of Embedded Stellar-Mass Black Holes in AGN Disks

Stellar-mass black holes (sBHs) embedded in active galactic nucleus (AGN) disks may affect X-ray variability through magnetic reconnection. As sBHs migrate and accumulate near migration traps, they disturb the disk magnetic field and trigger reconnection events that heat the disk and eject plasma into the overlying corona. The injected plasma dissipates kinetic energy and can trigger the release of magnetic energy already stored in the corona. We calculate the resulting coronal X-ray emission and the disk ultraviolet (UV) variability, including the disk thermal response and reprocessing of incident X-rays. We find that embedded sBHs can initially enhance short-timescale X-ray variability, but the variability becomes suppressed as more sBHs accumulate in the disk. At higher mass accretion rates through AGN disks, this suppression appears earlier. As sBH-associated reconnection events become more frequent, their active regions increasingly overlap, reducing the magnetic energy available to each event from the corona. We also find that variations in the disk ultraviolet (UV) emission follow the X-ray variations with a shorter delay than in the model without sBHs. These results suggest that a growing population of embedded sBHs does not necessarily produce stronger short-timescale X-ray variability.

astro-ph.HE↗

arXiv2026

A magnetar-powered jet-wind outflow in gamma-ray burst-associated supernovae: Application to the thermal components of GRB 060218-SN 2006aj

A rapidly rotating magnetar formed in the collapse of a massive star may release its spin-down power through both a collimated polar jet and a quasi-isotropic magnetar wind. With its long-lasting soft X-ray blackbody component and the double-peaked UV/optical light curves of SN 2006aj, GRB 060218-SN 2006aj provides a useful test case for such a two-component energy-injection scenario. We developed a magnetar-powered jet-wind model in which the two outflows interact with homologously expanding SN ejecta, driving forward shocks that produce shock-breakout emission and subsequent magnetar-powered thermal emission. We first used the jet component to fit the 0.3-10 keV blackbody flux and temperature evolution of GRB 060218 and subsequently added the wind component to model the UV/optical light curves of SN 2006aj. We find that the soft X-ray blackbody component can be reproduced mainly by shock-breakout emission from the polar ejecta driven by the jet. The double-peaked UV/optical light curves are instead produced by the interaction between the quasi-isotropic magnetar wind and a more massive ejecta component. The first optical peak is dominated by wind-driven shock-breakout emission, whereas the broader and later emission is powered mainly by the subsequent magnetar-powered thermal component. Our results suggest a two-component magnetar-engine picture for GRB 060218-SN 2006aj, in which the X-ray thermal emission and the UV/optical double-peaked evolution arise from different energy-injection channels of the same central engine.

astro-ph.HE↗

arXiv2026

Migration Traps as Variability Attractors. I. Optical/UV Signatures of Embedded Stellar-Mass Black Holes in Active Galactic Nucleus Disks

We investigate whether embedded stellar-mass black holes (sBHs) in active galactic nucleus (AGN) disks can leave observable optical/UV variability signatures through migration-trap-driven magnetic heating. This mechanism operates when sBHs migrating toward torque-balance radii pile up near migration traps, triggering localized, stochastic magnetic reconnection that heats the disk atmosphere. It is potentially important because it provides a physical source of non-coronal disk heating and directly links optical/UV continuum variability to otherwise hidden compact-object populations. By coupling a one-dimensional sBH population synthesis model with a corona-heated accretion-disk reprocessing variability framework, we show that migration traps concentrate sBHs at preferred radii and generate localized, stochastic reconnection heating. The resulting heating is self-regulated: sBH pile-ups enhance the reconnection rate, while gap opening reduces the local gas density and partially suppresses the reconnection power. This heating produces excess short-timescale optical/UV variability, flattened short-term structure functions, and deviations from the standard $τ\proptoλ^{4/3}$ lag-wavelength relation, which describes the time delay between variability at different wavelengths for a standard thin accretion disk. These signatures are strongest at low-to-moderate Eddington ratios, and related observations could provide indirect evidence for embedded compact-object populations in AGN disks.

astro-ph.GA↗

arXiv2026

A Unified Model for the Emission of Supernova-Associated Fast X-ray Transients: Case Studies of EP240414a, EP250108a, and GRB~171205A

The Einstein Probe (EP) has detected several Fast X-ray Transients (FXTs) associated with broad-lined Type Ic supernovae (SNe), including EP240414a and EP250108a. The observations reveal common features among these FXTs, but the corresponding physical origin remains debated. By comparing the FXTs with low-luminosity gamma-ray bursts (e.g., GRB 171205A), we propose a unified model that explains the common features in these events. In this model, a rapidly spinning magnetar generates a collimated Poynting flux-dominated jet and an isotropic wind. As the jet propagates through the stellar envelope, it generates a hot cocoon. In addition, a pulsar wind nebula (PWN) is formed during the interaction of the wind and the ejecta. As the surrounding cocoon gradually becomes transparent, the emission from the PWN escapes and is observed. This model provides a unified explanation for the observations: (1) Early thermal emission originates from the cocoon; (2) Mid-term non-thermal emission comes from the PWN; (3) Late-term emission originates from SNe driven by $^{56}$Ni radioactive decay and magnetar. (4) The X-ray afterglows originate from the structured jet. Our research thus provides a natural explanation for the observed thermal-to-nonthermal evolution in such FXTs and reveals their shared physical origin with some GRB-SNe.

astro-ph.HE↗

arXiv2026

A high-energy neutrino flare associated with nearby bright interacting supernova SN 2021foa

While core-collapse supernovae have been widely discussed as potential neutrino sources, definitive observational evidence has remained elusive. In this work, we report evidence of high-energy neutrino emission in the direction of supernova SN 2021foa, which is one of the closest and brightest interacting supernovae observed to date. Using the second data release of muon track data from the IceCube Neutrino Observatory, we conducted a time-dependent analysis and identified a neutrino clustering that temporally coincides with the optical peak of SN 2021foa, occurring approximately 16 to 22 days after the discovery date, with a maximum test statistic of $\sim 28.2$. Monte Carlo simulations indicate that the probability of observing such a neutrino excess by chance is $\sim6.7 \times 10^{-5}$, corresponding to a significance of $\sim4.0\,σ$. The spatial and temporal correlation strongly suggests that the neutrinos originate from the supernova. SN 2021foa is a unique "flip-flop" supernova; its spectra repeatedly transitioned between hydrogen-rich (Type IIn) and helium-rich (Type Ibn) phases within 50 days post-peak, reflecting a violent and complex mass-loss history of its progenitor. The inferred neutrino energy exceeds the optical radiative energy and ejecta kinetic energy of the supernova by orders of magnitude, suggesting that the neutrino emission is likely powered by a delayed central engine driving a jet that is choked within the dense circumstellar medium.

astro-ph.HE↗

arXiv2026

Multi-wavelength Emission for a Post-merger Magnetar: The Magnetar-Driven Poynting Jet and Its Associated Pulsar Wind Nebula

A newborn, rapidly rotating magnetar may form in a binary neutron star merger and drive a Poynting-flux-dominated relativistic jet. As the jet propagates outward, a forward shock (FS) and a reverse shock (RS) are formed, inflating a pulsar wind nebula (PWN) between them. We present a systematic study of the emission from both the PWN and the jet, whose magnetic energy is subject to dissipation. By following the dynamics of the jet-ejecta-PWN system, we find that, in most cases, the RS is long-lived: it first lags behind the contact discontinuity and eventually coincides with both the contact discontinuity and the FS after the jet breakout into the external medium. As a result, the emission exhibits a characteristic temporal evolution. Depending on the optical depth, the emission is initially dominated by thermal radiation from the optically thick ejecta, then by a jet-powered X-ray plateau once the system becomes optically thin, and finally by synchrotron and inverse-Compton radiation from the PWN FS at late times. In particular, external inverse-Compton scattering of jet photons by the FS naturally produces a late-time GeV bump together with a substantial TeV component. Our model can simultaneously account for early thermal emission, X-ray plateaus, and late-time GeV excesses in merger-driven gamma-ray bursts, and also indicates that post-merger magnetar-driven PWNs are potential TeV photon sources.

astro-ph.HE↗

arXiv2026

Could the interaction of jet and SN ejecta be the cause of X-ray knots observed in a radio galaxy?

We investigate the interaction between relativistic jets and supernova (SN) ejecta as a potential origin of X-ray knots in radio galaxies, employing knot A in M 87 as a test case. By modeling the dynamical evolution of the interaction, we evaluate this scenario based on particle acceleration efficiency and spatial morphology. Our modeling indicates that the ejecta shock expands to only ~ 30 pc, which is inconsistent with the observed spatial scale of knot A (~ 60 pc). In contrast, the jet shock can successfully reproduce the observed scale after approximately 3000 yr, with the ejecta being accelerated to a bulk velocity of β~ 0.43. We fit the multi-wavelength spectral energy distribution (SED) using a one-zone leptonic framework, attributing the X-rays to synchrotron radiation from electrons accelerated up to~1 PeV at the jet shock. The derived magnetic field is approximately 70 uG in the SN ejecta rest frame, which is significantly below the equipartition value. Protons may be accelerated up to ~ EeV, supporting the hypothesis that the jets of radio galaxies (RGs) may be the potential site for ultra-high-energy cosmic-ray (UHECR) acceleration within the framework of the jet-ejecta interaction.

astro-ph.HE↗

arXiv2026

Stellar Wind-Blown Bubbles as Environments for Late-Time Rebrightening of Gamma-Ray Burst Afterglows

We presented the multi-wavelength afterglow fitting results for three events that exhibit late afterglow rebrightening behavior: EP240414a ($z=0.401$), GRB 240529A ($z=2.695$), and GRB 240218A ($z=6.782$), which span a broad range of redshifts, from the local to the high-redshift universe.We prove that the peculiar afterglow light curves of three bursts can be well fitted by structured jets propagated in free-to-shocked stellar wind environment of stellar wind blown bubbles. This scenario offers a self-consistent explanation for the observed subclass of afterglows that exhibit rebrightening that is characterized by steep rises and rapid decays. It also provides a unified solution for such events and offers pathways to study both the jet generation mechanism and the propagation process of jets through the envelope of the progenitor. This study reveals that the structured jets produced by such events exhibit a narrow jet core and a steep angle-dependent energy decay index, suggesting highly magnetized jets. The derived transition radii from free stellar winds to shocked stellar winds for all three events are smaller than 0.5 pc, with statistical analysis of similar events indicating a median value of 0.1 pc, which conflicts with numerical simulation results. We anticipate that future observations by EP and SVOM missions will enhance the understanding of analogous events and further reveal information about progenitors and their circum-environments.

astro-ph.HE↗

arXiv2025

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

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.

astro-ph.HE↗

arXiv2025

GRB 240825A: Early Reverse Shock and Its Physical Implications

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.

astro-ph.HE↗

arXiv2025

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

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.

astro-ph.HE↗

arXiv2025

Radiation Spectrum of the Photospheric Emission for a Turbulent Relativistic Jet

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.

astro-ph.HE↗

arXiv2025

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

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.

astro-ph.HE↗

arXiv2025

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

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 $-1$.

astro-ph.HE↗

arXiv2024

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

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.

astro-ph.HE↗

arXiv2024

Probing blackbody components in gamma-ray bursts from black hole neutrino-dominated accretion flows

A stellar-mass black hole (BH) surrounded by a neutrino-dominated accretion flow (NDAF) is generally considered to be the central engine of gamma-ray bursts (GRBs). Neutrinos escaping from the disk will annihilate out of the disk to produce the fireball that could power GRBs with blackbody (BB) components. The initial GRB jet power and fireball launch radius are related to the annihilation luminosity and annihilation height of the NDAFs, respectively. In this paper, we collect 7 GRBs with known redshifts and identified BB components to test whether the NDAF model works. We find that, in most cases, the values of the accretion rates and the central BH properties are all in the reasonable range, suggesting that these BB components indeed originate from the neutrino annihilation process.

astro-ph.HE↗

arXiv2024

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

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.

astro-ph.HE↗

arXiv2024

GRB 221009A/SN 2022xiw: A Supernova Obscured by a Gamma-Ray Burst Afterglow?

We present optical photometry for the afterglow of GRB 221009A, in some respects the most extraordinary gamma-ray burst (GRB) ever observed. Good quality in the R-band light curve is obtained, covering 0.32-19.57 days since the Fermi-GBM trigger. We find that a weak bump emerges fromthe declining afterglow at $t \approx 11$ days; a supernova (SN) may be responsible. We use a smooth broken power-law and $^{56}\mathrm{Ni}$ model to fit the light curve. The best-fitting results reveal that the SN ejected a total mass of $M_\mathrm{ej} = 3.70 M_\odot$, a $^{56}\mathrm{Ni}$ mass of $M_\mathrm{Ni} = 0.23 M_\odot$, and a kinetic energy of $E_\mathrm{SN,K} = 2.35 \times 10^{52} \mathrm{erg}$. We also compare GRB 221009A with other GRB-SN events based on a GRB-associated SN sample, and find that only SN 2003lw and SN 2011kl can be obviously revealed in the afterglow of GRB 221009A by setting these objects at its distance. This suggests that a supernova (SN 2022xiw) is possibly obscured by the brighter afterglow emission from GRB 221009A.

astro-ph.HE↗