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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 at α ∼ +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 index α and peak energy E p with flux. For the α − F relationship, we employ F = F 0 e (3.00±0.10) α to describe it, whereas the E p− F relationship 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. [ABSTRACT FROM AUTHOR]

Many studies have shown that the X-ray flares in gamma-ray bursts (GRBs) have similar properties to the prompt emission pulses that occur in GRBs, suggesting that they may come from the same origin. We attempt to extend the evolution behavior that exists among GRBs to within individual GRBs. By selecting 12 GRBs with both multipulses and multiflares, we systematically study the overall evolution behaviors of the pulses and flares that occur within GRBs, including the width (w), peak time (t peak), rise time (t rise), decay time (t decay), and spectral lag. We find that correlated relationships exist within the GRBs, even if the overall evolution slopes of the pulses and flares in different GRBs are different. We also study the relations between the full pulse width (ω), the ratio of the rising width to the decay width (r / d), and the energy (E) of multipulses and multiflares within GRBs. It is found that there is a power-law anticorrelation between ω and E and a power-law correlation between r / d and E, with the mean values of the two power-law indexes being −0.42 and 0.07, respectively, which are very close to the values that are obtained for the prompt emission pulses. In addition, we find that the percentages of the positive lags for pulses and flares are 83% and 92%, respectively, with the lags of the flares being much larger than those of the pulses. Our results indicate that the overall evolution behaviors of the pulses and flares within individual GRBs are similar to the evolution behavior among GRBs, and that flares are low-energy extensions of pulses, providing further evidence that both come from the same origin. [ABSTRACT FROM AUTHOR]

The jet composition in gamma-ray bursts (GRBs) is still an unsolved issue. We try to provide some clues to the issue by analyzing the spectral properties of GRB 160509A and GRB 130427A with a main burst and a postburst. We first perform Bayesian time-resolved spectral analysis and compare the spectral components and spectral properties of the main bursts and postbursts of the two bursts and find that both bursts have the thermal components, and the thermal components are mainly found in the main bursts, while the postbursts are mainly dominated by the nonthermal components. We also find that the low-energy spectral indices of some time bins in the main bursts of these two GRBs exceed the so-called synchronous dead line, and in the postburst, only GRB 160509A has four time bins exceeding the dead line, while none of GRB 130427A exceed the dead line. We then constrain the outflow properties of both bursts and find that the main bursts is consistent with the typical properties of photosphere radiation. Therefore, our results support the transition of the GRB jet component from the fireball to the Poynting-flux-dominated jet. Finally, after analyzing the correlation and parameter evolution of the spectral parameters of the two bursts, we find that the correlations of the spectral parameters have different behaviors in the main bursts and postbursts. The parameter evolution trends of the main bursts and postbursts also show consistent and inconsistent behavior; therefore, we currently cannot determine whether the main bursts and postbursts come from the same origin. [ABSTRACT FROM AUTHOR]

We performed a time-resolved spectral analysis of 53 bright gamma-ray bursts (GRBs) observed by Fermi/GBM. Our sample consists of 1117 individual spectra extracted from the finest time slices in each GRB. We fitted them with the synchrotron radiation model by considering the electron distributions in five different cases: monoenergetic, single power law, Maxwellian, traditional fast cooling, and broken power law. Our results were further qualified through the Bayesian information criterion (BIC) by comparing with the fit by empirical models, namely, the so-called Band function and cutoff power-law models. Our study showed that the synchrotron models, except for the fast-cooling case, can successfully fit most observed spectra, with the single power-law case being the most preferred. We also found that the electron distribution indices for the single power-law synchrotron fit in more than half of our spectra exhibit flux-tracking behavior, i.e., the index increases/decreases with the flux increasing/decreasing, implying that the distribution of the radiating electrons is increasingly narrower with time before the flux peaks and becomes more spreading afterward. Our results indicate that the synchrotron radiation is still feasible as a radiation mechanism of the GRB prompt emission phase. [ABSTRACT FROM AUTHOR]