skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Time-resolved Spectral Properties of Fermi-GBM Bright Long Gamma-Ray Bursts
Abstract The prompt emission mechanism of gamma-ray bursts (GRBs) is still unclear, and the time-resolved spectral analysis of GRBs is a powerful tool for studying their underlying physical processes. We performed a detailed time-resolved spectral analysis of 78 bright long GRB samples detected by Fermi/Gamma-ray Burst Monitor. A total of 1490 spectra were obtained and their properties were studied using a typical Band-shape model. First, the parameter distributions of the time-resolved spectrum are given as follows: the low-energy spectral indexα∼ − 0.72, high-energy spectral indexβ∼ − 2.42, the peak energyEp∼ 221.69 keV, and the energy fluxF∼ 7.49 × 10−6erg cm−2s−1. More than 80% of the bursts exhibit the hardest low-energy spectral index α max exceeding the synchrotron limit (−2/3). Second, the evolution patterns ofαandEpwere statistically analyzed. The results show that for multi-pulse GRBs the intensity-tracking pattern is more common than the hard-to-soft pattern in the evolution of bothEpandα. The hard-to-soft pattern is generally shown in single-pulse GRBs or in the initial pulse of multi-pulse GRBs. Finally, we found a significant positive correlation betweenFandEp, with half of the samples exhibiting a positive correlation betweenFandα. We discussed the spectral evolution of different radiation models. The diversity of spectral evolution patterns indicates that there may be more than one radiation mechanism occurring in the GRB radiation process, including photospheric radiation and synchrotron radiation. However, it may also involve only one radiation mechanism, but more complicated physical details need to be considered.  more » « less
Award ID(s):
2011759
PAR ID:
10548229
Author(s) / Creator(s):
; ; ; ; ; ;
Publisher / Repository:
CAS and IOP Publishing Ltd
Date Published:
Journal Name:
Research in Astronomy and Astrophysics
Volume:
24
Issue:
2
ISSN:
1674-4527
Page Range / eLocation ID:
025006
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; (, The Astrophysical Journal)
    Abstract There is no consensus yet on whether the precursor and the main burst of gamma-ray bursts (GRBs) have the same origin, and their jet composition is still unclear. In order to further investigate this issue, we systematically search 21 Fermi GRBs with both a precursor and main burst for spectral analysis. We first perform Bayesian time-resolved spectral analysis and find that almost all the precursors and the main bursts (94.4%) exhibit thermal components and that the vast majority of them have a low-energy spectral index (α; 72.2%) that exceeds the limit of synchrotron radiation. We then analyze the evolution and correlation of the spectral parameters and find that approximately half of theα(50%) of the precursors and the main bursts evolve in a similar pattern, while peak energy (Ep; 55.6%) behaves similarly, and their evolution is mainly characterized by flux tracking; for theα−F(the flux) relation, more than half of the precursors and the main bursts (61.1%) exhibit roughly similar patterns; theEp−Frelation in both the precursor and main burst (100%) exhibits a positive correlation of at least moderate strength. Next, we constrain the outflow properties of the precursors and the main bursts and find that most of them exhibit typical properties of photosphere radiation. Finally, we compare the time-integrated spectra of the precursors and the main bursts and find that nearly all of them are located in similar regions of the Amati relation and follow the Yonetoku relation. Therefore, we conclude that main bursts are continuations of precursors and may share a common physical origin. 
    more » « less
  2. ; ; ; (, The Astrophysical Journal)
    Abstract This study presents detailed time-integrated and time-resolved spectral analysis of the Fermi Gamma-ray Burst Monitor observations of the bright GRB 231129C. The results reveal its distinct spectral characteristics, featuring a hard low-energy spectral index (α) and soft high-energy spectral index (β), similar to GRB 090902B, suggesting a possible dominance of thermal emission. Further analysis indicates that 92% of the spectral indices exceed the synchrotron “line of death,” with the hardest index atα∼ +0.44. Simultaneously, 53% of the spectra can be well fitted by the nondissipative photosphere model, supporting a potential origin from a nondissipative photosphere. Additionally, we observe strong correlations between the spectral indexαand peak energyEpwith flux. For theα−Frelationship, we employF=F0e(3.00±0.10)αto describe it, whereas theEp−Frelationship requires a smoothly bending power-law function. Based on the framework proposed by Hascoët et al. and Gao & Zhang, the jet characteristics of this burst were studied, revealing that both methods support the suitability of a pure fireball model for this GRB at small initial jet radii. 
    more » « less
  3. ; (, The Astrophysical Journal)
    Abstract The jet composition of gamma-ray bursts (GRBs), as well as how efficiently the jet converts its energy to radiation, are long-standing problems in GRB physics. Here, we reported a comprehensive temporal and spectral analysis of the TeV-emitting bright GRB 190114C. Its high fluence (∼4.4 × 10−4erg cm−2) allows us to conduct the time-resolved spectral analysis in great detail and study their variations down to a very short timescale (∼0.1 s) while preserving a high significance. Its prompt emission consists of three well-separated pulses. The first two main pulses (P1andP2) exhibit independently strong thermal components, starting from the third pulse (P3) and extending to the entire afterglow, the spectra are all nonthermal, and the synchrotron plus Compton upscattering model well interprets the observation. By combining the thermal (P1andP2) and the nonthermal (P3) observations based on two different scenarios (global and pulse properties) and following the method described in Zhang et al., we measure the fireball parameters and GRB radiative efficiency with little uncertainties for this GRB. A relevantly high GRB radiative efficiency is obtained based on both the global and pulse properties, suggesting that if GRBs are powered by fireballs, the efficiency can sometimes be high. More interestingly, though the observed parameters are individually different (e.g., the amount of mass loadingM), the radiative efficiency obtained fromP1(ηγ= 36.0% ± 6.5%) andP2(ηγ= 41.1% ± 1.9%) is roughly the same, which implies that the central engine of the same GRB has some common properties. 
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al (, The Astrophysical Journal Letters)
    Abstract We report observations of the optical counterpart of the long gamma-ray burst (GRB) GRB 230812B and its associated supernova (SN) SN 2023pel. The proximity (z= 0.36) and high energy (Eγ,iso∼ 1053erg) make it an important event to study as a probe of the connection between massive star core collapse and relativistic jet formation. With a phenomenological power-law model for the optical afterglow, we find a late-time flattening consistent with the presence of an associated SN. SN 2023pel has an absolute peakr-band magnitude ofMr= −19.46 ± 0.18 mag (about as bright as SN 1998bw) and evolves on quicker timescales. Using a radioactive heating model, we derive a nickel mass powering the SN ofMNi= 0.38 ± 0.01M⊙and a peak bolometric luminosity ofLbol∼ 1.3 × 1043erg s−1. We confirm SN 2023pel’s classification as a broad-line Type Ic SN with a spectrum taken 15.5 days after its peak in therband and derive a photospheric expansion velocity ofvph= 11,300 ± 1600 km s−1at that phase. Extrapolating this velocity to the time of maximum light, we derive the ejecta massMej= 1.0 ± 0.6M⊙and kinetic energy E KE = 1.3 − 1.2 + 3.3 × 10 51 erg . We find that GRB 230812B/SN 2023pel has SN properties that are mostly consistent with the overall GRB-SN population. The lack of correlations found in the GRB-SN population between SN brightness andEγ,isofor their associated GRBs across a broad range of 7 orders of magnitude provides further evidence that the central engine powering the relativistic ejecta is not coupled to the SN powering mechanism in GRB-SN systems. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, The Astrophysical Journal Letters)
    Abstract We present photometric and spectroscopic observations of the extraordinary gamma-ray burst (GRB) 221009A in search of an associated supernova. Some past GRBs have shown bumps in the optical light curve that coincide with the emergence of supernova spectral features, but we do not detect any significant light-curve features in GRB 221009A, nor do we detect any clear sign of supernova spectral features. Using two well-studied GRB-associated supernovae (SN 2013dx, M r , max = − 19.54 ; SN 2016jca, M r , max = − 19.04 ) at a similar redshift as GRB 221009A (z= 0.151), we modeled how the emergence of a supernova would affect the light curve. If we assume the GRB afterglow to decay at the same rate as the X-ray data, the combination of afterglow and a supernova component is fainter than the observed GRB brightness. For the case where we assume the best-fit power law to the optical data as the GRB afterglow component, a supernova contribution should have created a clear bump in the light curve, assuming only extinction from the Milky Way. If we assume a higher extinction ofE(B−V) = 1.74 mag (as has been suggested elsewhere), the supernova contribution would have been hard to detect, with a limit on the associated supernova of M r , max ≈ − 19.54. We do not observe any clear supernova features in our spectra, which were taken around the time of expected maximum light. The lack of a bright supernova associated with GRB 221009A may indicate that the energy from the explosion is mostly concentrated in the jet, leaving a lower energy budget available for the supernova. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email