Precursors in Short Gamma-ray Bursts as a Possible Probe of Progenitors

TL;DR

This study identifies and analyzes precursors in short gamma-ray bursts, revealing their spectral and temporal characteristics, and suggests they could provide insights into the properties of progenitor systems like binary mergers.

Contribution

It presents a comprehensive analysis of 18 SGRB precursors, highlighting their spectral softness, temporal features, and potential as probes of progenitor properties, which is a novel approach.

Findings

Precursors are generally shorter than main bursts and occur before the main emission.

Precursor flux tends to increase as the main burst brightens.

Precursor spectra are slightly softer and often non-thermal.

Abstract

We extract 18 candidate short gamma-ray bursts (SGRBs) with precursors from 660 SGRBs observed by {\em Fermi} and {\em Swift} satellites, and carry out a comprehensive analysis on their temporal and spectral features. We obtain the following results: (1) For a large fraction of candidates, the main burst durations are longer than their precursor durations, comparable to their quiescent times from the end of precursors to the beginning of their main bursts. (2) The average flux of precursors tends to increase as their main bursts brighten. (3) As seen from the distributions of hardness ratio and spectral fitting, the precursors are slightly spectrally softer with respect to the main bursts. Moreover, a significant portion of precursors and all main bursts favor a non-thermal spectrum. (4) The precursors might be a probe of the progenitor properties of SGRBs such as the magnetic field strength and the crustal equation of state if they arise from some processes before mergers of binary compact objects rather than post-merger processes.