arXiv subjects

Xue-Zhao Chang

Publications and source records attributed to Xue-Zhao Chang.

6 recordsLinked to original sources

arXiv2026

Identifying the poynting-flux-dominated outflow of Fermi GRBs with non-thermal spectrum and its energy-resolved light curve fitting

The jet compositions of gamma-ray bursts (GRBs) are very important to understand the energy dissipation and radiation mechanisms, but it remains an open question in GRB physics. In this paper, we present a systematic analysis to search for 88 bright GRBs that include a total of 129 pulses observed by Fermi/GBM with redshift measured, and extract the spectra of each pulse with Band function (Band), cutoff power-law (CPL), blackbody (BB), non-dissipative photospheric (NDP), Band+BB, as well as CPL+BB. We find that 80 pulses, 35 pulses, and 14 pulses present purely non-thermal, hybrid, and thermal spectra, respectively. By focusing on those 80 pulses with purely non-thermal spectra, one can estimate the lower limits of magnetization factor ($σ$) via suppressing the pseudo-thermal component. It is found that 30 pulses in 21 GRBs are the lower limit of $σ>5$ at the photosphere by adopting $R_{0}=10^{10}$ cm. It suggests that at least the outflow of those GRB jets with high $σ$ is dominated by Poynting-flux. On the other hand, we also perform the light curve fitting with a fast-rise-exponential-decay (FRED) model for 15 bright GRBs with a high magnetization factor in our sample, and find that a correlation between pulse width ($w$) and energy of 13 GRBs really exists in their energy-resolved light curves. It is also a piece of independent evidence for those GRBs with a high value $σ$ to support the origin of the Poynting flux outflow.

astro-ph.HE↗

arXiv2025

Evidence for the transition from thermal to non-thermal emission in the prompt emission of GRB 161117A

GRB 161117A is a long-duration GRB with three main overlapping peaks. By analyzing the time-resolved spectra of its data observed with the Gamma-Ray Burst Monitor (GBM) on board the Fermi mission, we find that the spectral evolution shows a transition from thermal (single BB) to hybrid (PL$+$BB), and finally to non-thermal (Band and CPL) emissions. Such a transition suggests that the jet composition of GRB 161117A should be changed from a fireball to a Poynting-flux-dominated jet. The bulk Lorentz factor ($Γ_{\rm ph}$), radii ($R_{\rm ph}$ and $R_{0}$), magnetization factor at the central engine ($σ_0$), and dimensionless entropy ($η$) of the outflow can be inferred by invoking the observed quasi-thermal component within two models (e.g., pure fireball and hybrid). It is found that $Γ_{\rm ph}$ seems to be tracking with the light curve, and $R_{0}$ remains a constant at $\sim$ $10^{8}$ cm. The low magnetization ($1+σ_0 \sim$ 1) and high dimensionless entropy ($η\gg$ 1) during the first seven time-intervals suggest to be a pure fireball outflow. Moreover, we also estimate the lower limit of magnetization parameter at the photosphere radius ($σ_{\rm ph}\sim 1.4$ and 0.75) for late phase via the non-thermal spectra, and it indicates that the particle acceleration mechanism is dominated by internal shocks rather than magnetic dissipation processes. Finally, the $ν\barν$ annihilation mechanism of NDAF model to explain the thermal emission of GRB 161117A is also discussed.

astro-ph.HE↗

arXiv2025

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

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.

astro-ph.HE↗

arXiv2024

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

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.

astro-ph.HE↗

arXiv2024

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

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.

astro-ph.HE↗

arXiv2022

Thermal and nonthermal emission from a peculiar long-duration GRB 211211A

Long-duration GRB 211211A that lacks a supernova emission even down to very stringent limits at such a low redshift $z=0.076$ and is associated with kilonova emission, suggests that its physical origin is from a binary compact star merger. By reanalyzing its data observed with the Gamma-Ray Burst Monitor on board the Fermi mission, we find that both time-integrated and time-resolved spectra can be fitted well by using a 2SBPL plus blackbody (2SBPL+BB) model in the prompt emission. The bulk Lorentz factors ($Γ_{\rm ph}$) of the outflow can be inferred by invoking the observed thermal emission at the photosphere radius within a pure fireball model, and we find out that the temporal evolution of $Γ_{\rm ph}$ seems to be tracking with the light curve. The derived values of $Γ_{\rm ph}$ are also consistent with the $Γ_{\rm ph}$-$L_{γ, \rm iso}$/$E_{γ, \rm iso}$ correlations that had been found in other bursts. Moreover, we also calculate the magnetization factor $σ_{0}$ in the central engine and $σ_{\rm ph}$ at the photosphere radius within the framework of a hybrid jet model, and find that the values of both $1+σ_{\rm 0}$ and $1+σ_{\rm ph}$ are larger than 1 for different time slices. It suggests that at least the Poynting-flux component is indeed existent in the outflow. If this is the case, one possible physical interpretation of thermal and nonthermal emissions in GRB 211211A is from the contributions of both $ν\barν$ annihilation and the Blandford-Znajek mechanisms in the relativistic jet when a stellar mass black hole resides in the central engine.

astro-ph.HE↗