Overall spectral properties of prompt emissions with diverse segments in Swift/BAT short gamma-ray bursts

Abstract

Owing to a lack of multiple components of prompt γ-ray emissions in short gamma-ray bursts (sGRBs), how these distinct components are correlated remains unclear. In this paper we investigate the spectral and temporal properties of precursors, main peaks, and extended emissions in 26 sGRBs including GRB 170817A. It has been found that peak energies (Ep) in each pulse are uncorrelated with the pulse duration (tdur). Meanwhile, we find that there is no obvious correlation between peak energy and energy fluence. Interestingly, there is no obvious spectral evolution from earlier precursors to later extended emissions in view of the correlations of tdur with either the Ep or the low-energy spectrum index, α. A power-law correlation between the average flux (Fp) and the energy fluence (Sγ), log Fp = (0.62 ± 0.07) log Sγ + (0.27 ± 0.07), is found to exist in the individual segments instead of mean peaks. Furthermore, we also find that the main peaks are on average brighter than the precursors or the extend emissions by about one order of magnitude. On the basis of all the above analyses, we can conclude that three emissive components could share the same radiation mechanisms, but that they might be dominated by diverse physical processes.