arXiv subjects

Jin-Jun Geng

Publications and source records attributed to Jin-Jun Geng.

At least 37 records · Page 2Linked to original sources

arXiv2025

A Statistical Study of the Gamma-Ray Burst and Supernova Association

The association between long gamma-ray bursts (LGRBs) and core-collapse supernovae (SNe) has been well established since the discovery of SN 1998bw, which was linked to the low-luminosity LGRB 980425. However, long-term monitoring of several well-localized, low-redshift LGRBs has yielded compelling evidence for the absence of accompanying SNe. Notably, two long bursts, GRB 211211A and GRB 230307A, show signatures consistent with kilonova emission from compact binary mergers, indicating that at least some long events may originate from progenitors other than core-collapse SNe. In this study, we conduct a comparative analysis of two samples of LGRBs, i.e., LGRBs with and without SN associations, to investigate the differences that may reveal intrinsic distinctions in their progenitors. A detailed examination of their prompt emission properties, host galaxy environments, and event rates is performed. While the two samples exhibit considerable overlap in most observed properties, a significant discrepancy in their event rate is revealed. LGRBs without SN association have an event rate that aligns well with the star formation rate, whereas that of SN-associated LGRBs differs significantly. It indicates that LGRBs without an SN association may constitute a distinct subclass with intrinsically different progenitors.

astro-ph.HE↗

arXiv2025

Axial current as the origin of quantum intrinsic orbital angular momentum

We show that the axial current density is the physical origin (generator) of quantum intrinsic orbital angular momentum (IOAM). Without the axial current, the IOAM of particles vanishes. Broadly speaking, we argue that the spiral or interference characteristics of the axial current density determine the occurrence of nonlinear or tunneling effects in any spacetime-dependent quantum systems. Our findings offer a comprehensive theoretical framework that addresses the limitations of Keldysh's ionization theory and provides new insights into the angular momentum properties of quantum systems, particularly in tunneling-dominated regimes. Using Wigner function methods, fermionic generalized two-level model, and Berry phase simulations, we predict that IOAM effect can persist even in pure quantum tunneling processes. These results open the door for experimental verification of IOAM effects in future high-intensity QED experiments, such as those using X-ray free electron lasers.

hep-ph↗

arXiv2025

Magnetic Reconnection as a Potential Driver of X-ray Variability in Active Galactic Nuclei

We present a systematic analysis on the X-ray variability in 13 bright quasars at z > 4.5, combining recent Swift observations from 2021 to 2023 and archival multi-epoch observations. Upper limits of the luminosity measurements were included in the analysis by using the Kaplan-Meier estimator method. It is found that the high-z quasars exhibit X-ray variability on both short-term (hours-to-days) and intermediate-term (weeks-to-months) timescales, with short-term variability dominating the overall variation. A linear correlation exists between the global mean ($μ_{\mathrm{L_{2-10\,keV}}}$) and standard deviation ($σ_{\mathrm{L_{2-10\,keV}}}$) of X-ray luminosities, which is independent of the X-ray photon index and optical-to-X-ray spectral slope. The localized stochastic magnetic reconnection mechanism is strongly favored, which can naturally lead to a scale-invariant power-law energy distribution and satisfactorily explain the correlation. The $σ$-$μ$ correlation parallels with the well-documented rms-flux relation of low-z active galactic nuclei (AGNs), implying the magnetic reconnection mechanism could drive short-timescale X-ray variability in both high- and low-z AGNs. The highest-z quasar in our sample, J142952+544717 (z = 6.18), shows a luminosity distribution extending to ${10}^{47}\ \rm{erg\ {s}^{-1}}$ with a not conspicuous median luminosity. On the other hand, J143023+420436 (z = 4.7), which hosts the most relativistic jet among known high-z blazars, is dominated in the high-luminosity regime (${10}^{47}\ \rm{erg\ {s}^{-1}}$ ), making it an ideal target for multi-wavelength follow-up observations. J090630+693030 is found to have a rest-frame period of 182.46 days and J143023+420436 has a period of 16.89 days, both could be explained by the global evolution of plasmoid chains, in which magnetic islands formed during reconnection may merge successively.

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

Anisotropy of core-collapse supernovae effected by AGN disks

Active galactic nucleus (AGN) disk provide dense environments to influence on the star formation, evolution, and migration. In AGN disks, pressure gradients and migration accelerations could create the anisotropy of the core-collapse supernovae (CCSNe) when the massive stars explode at the end of their lives. In this study, we construct the equilibrium equations by considering the above two factors and then compute the light curves for three types of progenitor stars at different locations of AGN disks for the different supermassive black hole (SMBH) masses, accretion efficiencies, explosion energies, and masses of ejecta. The results show that the migration acceleration has more significant effects on the anisotropic explosions than the pressure gradients of the AGN disks. The anisotropic luminosities are pronounced at large radii, and massive SMBHs would suppress the anisotropy and reduce the total luminosity.

astro-ph.HE↗

arXiv2025

Softness Ratio of SWIFT Gamma-ray Bursts and Relevant Correlations

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

astro-ph.HE↗

arXiv2025

GRB Timing: Decoding the Hidden Slow Jets in GRB 060729

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

astro-ph.HE↗

arXiv2025

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

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

astro-ph.HE↗

arXiv2025

The Soft X-ray Aspect of Gamma-ray Bursts in the Einstein Probe Era

The Einstein Probe (EP) satellite, dedicated at time-domain high-energy astrophysics and multi-messenger astronomy, was recently launched and successfully put into operation. The wide-field X-ray telescope (WXT, 0.5-4 keV) onboard has identified multiple gamma-ray burst (GRB) events, with an average duration of several hundred seconds. This duration is several times longer than the average duration of long gamma-ray bursts (LGRBs) detected by the Neil Gehrels Swift Observatory, which typically stands at several tens of seconds. Additionally, EP has detected some unknown X-ray transients whose connection to GRBs is uncertain, due to the absence of gamma-ray counterparts and efficient follow-up observation at multi-wavelengths. Several main factors could account for the longer time, including the Doppler effect of off-axis viewing, the spectral lag effect of the synchrotron spectrum of cooling electrons, and some unknown prolonged intrinsic X-ray activities. Our studies indicate that EP GRBs may primarily consist of off-axis viewed bursts, forming a unique population among the GRB zoo, yet the intrinsic origin for the specific bursts could not be excluded. By analyzing the statistical properties of the historical LGRB samples, we explored observable properties of on-axis and off-axis LGRBs in the soft X-ray band. The predicted characteristics of off-axis viewed GRBs, including the duration, energy fluence, low-energy spectral index, and the slopes of Amati and Yonetoku relations, could be tested with a larger sample of GRB events detected by EP in the future.

astro-ph.HE↗

arXiv2025

Generalized quantum two level model and its application in astrophysics

Complicated time-dependent curved spacetime and electric field are involved in many astrophysical situations, including the early universe, Hawking radiation, the Schwinger effect, and gravitational pair production. In this Letter, a generalized quantum two-level model (GQTLM) is developed, which is applicable to arbitrary time-dependent curved spacetime and electric field. The model is found to be consistent with quantum kinetic theory, and is characterized by its simplicity and versatility. The momentum distribution of particles and the effects of gravitational distortions can be correctly described. Quantum properties concerning vortex structures, such as the intrinsic orbital angular momentum of particles and antiparticles can also be conveniently calculated. The model is expected to significantly advance the quantum exploration of the universe. It could refine the prediction of primordial gravitational waves and relevant non-Gaussian signals, extend the calculation of Hawking radiation to general black hole configurations, help to distinguish neutron stars from strange quark stars, and elucidate the gravitational pair production mechanism.

gr-qc↗

arXiv2025

Bounding the photon mass with gravitationally lensed fast radio bursts

The gravitational time delays of macro-lenses can be used to constrain the rest mass of the photon with high accuracy. Assuming a point-mass $+$ external shear lens model, we prove that an upper limit of the photon mass can be derived directly from two observables--the time delay $Δt$ and the leading-to-trailing flux ratio $R$ of strongly lensed fast radio bursts (FRBs). Using the observed values of $Δt$ and $R$ of a lensed FRB candidate, i.e., FRB 20190308C, as a reference, we obtain a strict upper limit of the photon mass between $m_γ< 5.3 \times {10}^{-42}\,\rm kg$, for a given external shear strength of $γ' = 0.01$, and $m_γ < 2.1 \times 10^{-41}-2.4 \times 10^{-42}\,\text{kg}$, within the external shear range of $0<γ'<1$. This provides the most stringent limit to date on the photon mass through gravitational lensing time delays, improving by 1 to 2 orders of magnitude the previous results obtained from lensed active galactic nuclei.

astro-ph.HE↗

arXiv2025

Intrinsic Pulse Widths of FRB 20121102A and Calculation of Broadening from Propagation and Instrumental Effects

The pulse widths of fast radio bursts are always broadened due to the scattering of the plasma medium through which the electromagnetic wave passes. The recorded pulse width will be further affected by the radio telescopes since the sampling time and the bandwidth cannot be infinitely small. In this study, we focus on the pulse widths of at least 3287 bursts detected from FRB 20121102A as of October 2023. Various effects such as the scattering broadening, the redshift-induced broadening and the instrumental broadening are examined. At a redshift of 0.193, the pulse width is broadened by a factor of approximately 0.16 due to cosmological time dilation. It is found that the instrumental broadening only contributes a fraction of $10^{-3}$ -- $10^{-1}$ to the observed pulse width. The scattering broadening is even smaller, which constitutes a tiny fraction of $10^{-5}$ -- $10^{-2}$ in the observed pulse width. After correcting for these broadenings, the intrinsic pulse width is derived for each burst. The maximum and minimum pulse widths at different frequencies are highlighted. The intrinsic widths of most bursts are in a narrow range of 1 -- 10 ms, which leads to a quasi-linear correlation between the fluence and the peak flux. Besides, the mean value and the dispersion range of intrinsic pulse width are found to scale with the central frequency as $ν^{-1.2 \pm 0.2}$ and $ν^{-1.7 \pm 0.6}$, respectively.

astro-ph.HE↗

arXiv2024

GRB 240529A: A Tale of Two Shocks

Thanks to the rapidly increasing time-domain facilities, we are entering a golden era of research on gamma-ray bursts (GRBs). In this Letter, we report our observations of GRB 240529A with the Burst Optical Observer and Transient Exploring System, the 1.5-meter telescope at Observatorio Sierra Nevada, the 2.5-meter Wide Field Survey Telescope of China, the Large Binocular Telescope, and the Telescopio Nazionale Galileo. The prompt emission of GRB 240529A shows two comparable energetic episodes separated by a quiescence time of roughly 400 s. Combining all available data on the GRB Coordinates Network, we reveal the simultaneous apparent X-ray plateau and optical re-brightening around $10^3-10^4$ s after the burst. Rather than the energy injection from the magnetar as widely invoked for similar GRBs, the multi-wavelength emissions could be better explained as two shocks launched from the central engine separately. The optical peak time and our numerical modeling suggest that the initial bulk Lorentz factor of the later shock is roughly 50, which indicates that the later jet should be accretion-driven and have a higher mass loading than a typical one. The quiescence time between the two prompt emission episodes may be caused by the transition between different accretion states of a central magnetar or black hole, or the fall-back accretion process. A sample of similar bursts with multiple emission episodes in the prompt phase and sufficient follow-up could help to probe the underlying physics of GRB central engines.

astro-ph.HE↗

arXiv2024

Probing Thermal Electrons in GRB Afterglows

Particle-in-cell simulations have unveiled that shock-accelerated electrons do not follow a pure power-law distribution, but have an additional low-energy "thermal" part, which owns a considerable portion of the total energy of electrons. Investigating the effects of these thermal electrons on gamma-ray burst (GRB) afterglows may provide valuable insights into the particle acceleration mechanisms. We solve the continuity equation of electrons in the energy space, from which multi-wavelength afterglows are derived by incorporating processes including synchrotron radiation, synchrotron self-absorption, synchrotron self-Compton scattering, and gamma-gamma annihilation. First, there is an underlying positive correlation between temporal and spectral indices due to the cooling of electrons. Moreover, thermal electrons would result in the simultaneous non-monotonic variation in both spectral and temporal indices at multi-wavelength, which could be individually recorded by the 2.5-meter Wide Field Survey Telescope and Vera Rubin Observatory Legacy Survey of Space and Time (LSST). The thermal electrons could also be diagnosed from afterglow spectra by synergy observation in the optical (with LSST) and X-ray bands (with the Microchannel X-ray Telescope on board the Space Variable Objects Monitor). Finally, we use Monte Carlo simulations to obtain the distribution of peak flux ratio ($R_{\rm X}$) between soft and hard X-rays, and of the time delay ($Δt$) between peak times of soft X-ray and optical light curves. The thermal electrons significantly raise the upper limits of both $R_{\rm X}$ and $Δt$. Thus the distribution of GRB afterglows with thermal electrons is more dispersive in the $R_{\rm X} - Δt$ plane.

astro-ph.HE↗

arXiv2024

An optical-ultraviolet flare with absolute AB magnitude of -39.4 detected in GRB 220101A

Hyperluminous optical-ultraviolet fares have been detected in gamma-ray bursts and the luminosity record was held by naked-eye event GRB 080319B. Such fares are widely attributed to internal shock or external reverse shock radiation. Here, with a new method developed to derive reliable photometry from saturated sources of Swift/UVOT, we carry out time-resolved analysis of the initial white-band 150s exposure of GRB 220101A, a burst at a redshift of 4.618, and report a rapidly evolving optical-ultraviolet fare with a high absolute AB magnitude of -39.4$\pm$0.2. In contrast to GRB 080319B, the temporal behaviour of this new fare does not trace the gamma-ray activity. Instead of either internal shocks or reverse shock, this extremely energetic optical-ultraviolet fare is most likely to originate from the refreshed shocks induced by the late-ejected extremely energetic material catching up with the earlier-launched decelerating outflow. This finding reveals the diverse origins of the extremely energetic optical-ultraviolet fares and demonstrates the necessity of high-time-resolution observations at early times.

astro-ph.HE↗

arXiv2024

Repeating fast radio bursts produced by a strange star interacting with its planet in an eccentric orbit

FRB 180916 is an important repeating fast radio burst (FRB) source. Interestingly, the activity of FRB 180916 shows a well-regulated behavior, with a period of 16.35 days. The bursts are found to occur in a duty circle of about 5 days in each period. In this study, we suggest that the bursts of FRB 180916 are produced by a strange star interacting with its planet. The planet moves in a highly eccentric orbit around its compact host, with the periastron only slightly beyond the tidal disruption radius. As a result, the planet will be partially disrupted every time it passes through the periastron. The stripped material from the planet will be accreted by the strange star, falling to the polar cap region along the magnetic field lines and accumulated there. It will finally lead to a local collapse when the crust at the polar region is overloaded, triggering an FRB. The observed 16.35 day period corresponds to the orbital motion of the planet, and the 5 day duty circle is explained as the duration of the partial disruption near the periastron. The energy released in each local collapse event can be as high as $\sim 10^{42}~\rm {erg}$, which is large enough to account for typical FRBs even if the radiation efficiency is extremely low.

astro-ph.HE↗

arXiv2023

Coherent Cherenkov Radiation by Bunches in Fast Radio Bursts

Fast radio bursts (FRBs) are extragalactic radio transients with extremely high brightness temperature, which strongly suggests the presence of coherent emission mechanisms. In this study, we introduce a novel radiation mechanism for FRBs involving coherent Cherenkov radiation (ChR) emitted by bunched particles that may originate within the magnetosphere of a magnetar. We assume that some relativistic particles are emitted from the polar cap of a magnetar and move along magnetic field lines through a charge-separated magnetic plasma, emitting coherent ChR along their trajectory. The crucial condition for ChR to occur is that the refractive index of the plasma medium, denoted as $n_r$, must satisfy the condition $n_r^2 > 1$. We conduct comprehensive calculations to determine various characteristics of ChR, including its characteristic frequency, emission power, required parallel electric field, and coherence factor. Notably, our proposed bunched coherent ChR mechanism has the remarkable advantage of generating a narrower-band spectrum. Furthermore, a frequency downward drifting pattern, and $\sim100\%$ linearly polarized emission can be predicted within the framework of this emission mechanism.

astro-ph.HE↗

arXiv2023

Possible origin of AT2021any: a failed GRB from a structured jet

Searching for afterglows not associated with any gamma-ray bursts (GRBs) is a longstanding goal of transient surveys. These surveys provide the very chance of discovering the so-called orphan afterglows. Recently, a promising orphan afterglow candidate, AT2021any, was found by the Zwicky Transient Facility. Here we perform multi-wavelength fitting of AT2021any with three different outflow models, namely the top-hat jet model, the isotropic fireball model, and the structured Gaussian jet model. Although the three models can all fit the observed light curve well, it is found that the structured Gaussian jet model presents the best result, and thus is preferred by observations. In the framework of the Gaussian jet model, the best-fit Lorentz factor is about 68, which indicates that AT2021any should be a failed GRB. The half-opening angle of the jet and the viewing angle are found to be 0.104 and 0.02, respectively, which means that the jet is essentially observed on-axis. The trigger time of the GRB is inferred to be about 1000 s before the first detection of the orphan afterglow. An upper limit of 21.4% is derived for the radiative efficiency, which is typical in GRBs.

astro-ph.HE↗