Indication of Two Classes in the Swift Short Gamma-Ray Bursts from the XRT X-Ray Afterglow Light Curves

TL;DR

This paper identifies two distinct classes of Swift short gamma-ray bursts based on their X-ray afterglow durations, revealing differences in their properties and suggesting potential different progenitors.

Contribution

The study uncovers a new classification of short GRBs into short-lived and long-lasting X-ray afterglow groups, based on Swift XRT data, and discusses implications for their origins.

Findings

40% of S-GRBs have X-ray afterglows lasting less than 10,000 seconds

60% of S-GRBs exhibit long-lasting X-ray afterglows similar to long GRBs

None of the short-lived S-GRBs show extended emission in BAT energy range

Abstract

We present the discovery of two distinct classes in the Swift short duration gamma-ray bursts (S-GRBs) from the X-Ray Telescope (XRT) X-ray afterglow light curve. We find that about 40% of the Swift S-GRBs have an X-ray afterglow light curves which only lasts less than 10000 seconds after the burst trigger (hereafter short-lived S-GRBs). On the other hand, another 60% of S-GRBs have a long lasting X-ray afterglow light curve which resembles the long duration gamma-ray bursts. We also find that none of the short-lived S-GRBs shows the extended emission in the Burst Alert Telescope (BAT) energy range. We compare the burst properties for both the prompt emission and the afterglow, and discuss the possibility of different progenitors for the Swift short GRBs.