{\em Fermi}/GBM Short Gamma-ray Burst Catalog and Case Study for GRB 170817A/GW 170817

TL;DR

This paper presents a comprehensive catalog of short gamma-ray bursts observed by Fermi/GBM over nine years, analyzes their properties, identifies two light curve patterns, and studies the special case of GRB 170817A associated with GW 170817, suggesting different progenitors for different sGRB types.

Contribution

It provides the first extensive catalog of sGRBs with detailed analysis, including light curve patterns, spectral properties, and a case study of GRB 170817A, proposing different progenitor origins for sGRB subtypes.

Findings

Two light curve patterns identified: single and multiple episodes.

GRB 170817A is a soft, weak sGRB consistent with typical short GRB relations.

Potential existence of two distinct sGRB populations from different progenitors.

Abstract

Motivating by the discovery of association between GW 170817 and sGRB 170817A, we present a comprehensive analysis for sGRBs observed with Fermi/GBM in 9 operation years and study the properties of sGRB 170817A -like events. We derive a catalog of 275 typical sGRBs and 48 sGRB 170817A-like weak events from the GBM data of 2217 GRBs. We visibly identify two patterns of their light curve, single episode (Pattern I, 61\% of the SGRBs) and multiple episodes (Pattern II, 39\% of the SGRBs). Their duration distribution shows a tentative bimodal feature. Their spectra can be fitted with a cutoff power-law model, except for 4 sGRBs, and the spectral indices normally distribute at $\Gamma=0.69\pm 0.40$. Their $E_p$ values show a tentative bimodal distribution with peaks at 145 keV and 500 keV. No correlation among $T_{90}$, $E_p$, and $\Gamma$ is found. GRB 170817A is a soft, weak sGRB with $ E_{p}=124\pm 106$ keV, $L_{\rm iso}=(5.67\pm4.65)\times10^{46}\rm ~erg~s^{-1}$, and $E_{\rm iso}=(3.23\pm2.65)\times10^{46}\rm ~erg$. It follows the $E_{\rm iso}-E_{\rm p}$ relation of typical short GRBs. Its lightcurve is of Pattern II. Two lightcurve patterns, together with the potential two components in the $E_{\rm p}$ and $T_{90}$ distributions, we suspect that the current sample may include two distinct types of sGRBs from different progenitors. sGRB 170817A-like events may be from NS-NS mergers and those sGRBs with a Pattern I lightcurve may be from another distinct type of compact binary.