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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 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.
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Single-pulse Gamma-Ray Bursts Have Prevalent Hard-to-soft Spectral Evolution
Abstract We analyze the spectral evolution of 62 bright Fermi gamma-ray bursts with large enough signal-to-noise to allow for time-resolved spectral analysis. We develop a new algorithm to test for single-pulse morphology that is insensitive to the specific shape of pulses. Instead, it only checks whether or not there are multiple, isolated, or statistical significant peaks in the light curve. In addition, we carry out a citizen science test to assess light-curve morphology and spectral evolution. We find that, no matter the adopted assessment method, bursts characterized by single-peaked prompt emission light curves have a greater tendency to also have a consistently decaying peak energy or hard-to-soft spectral evolution. This contrasts with the behavior of multipeaked bursts, for which the tendency is to have a peak frequency that is not monotonically decreasing. We discuss this finding in the theoretical framework of internal/external shocks and find it to be consistent with at least some single-pulse bursts associated with particularly high-density environments.
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- Award ID(s):
- 1907955
- PAR ID:
- 10536617
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 972
- Issue:
- 1
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 83
- Size(s):
- Article No. 83
- Sponsoring Org:
- National Science Foundation
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