Catalog of Isolated Emission Episodes in Gamma-ray Bursts from Fermi, Swift and BATSE

TL;DR

This paper presents a large, automated catalog of isolated emission episodes in long gamma-ray bursts from Fermi, Swift, and BATSE, revealing that such episodes often occur before and after the main burst, extending our understanding of GRB activity.

Contribution

It provides the largest catalog of isolated emission episodes in long GRBs, extending the search window and systematically analyzing pre- and post-peak emissions with an automated method.

Findings

24% of GRBs have multiple isolated emission episodes.

11% have pre-peak events, 15% have post-peak events.

Activity often extends beyond the T90 duration of GRBs.

Abstract

We report a comprehensive catalog of emission episodes within long gamma-ray bursts (GRBs) that are separated by a quiescent period during which gamma-ray emission falls below the background level. We use a fully automated identification method for an unbiased, large scale and expandable search. We examine a comprehensive sample of long GRBs from the BATSE, Swift and Fermi missions, assembling a total searched set of 2710 GRBs, the largest catalog of isolated emission episodes so far. Our search extends out to [-1000s,750s] around the burst trigger, expanding the covered time interval beyond previous studies and far beyond the nominal durations (T90) of most bursts. We compare our results to previous works by identifying pre-peak emission (or precursors), defined as isolated emission periods prior to the episode with the highest peak luminosity of the burst. We also systematically search for similarly defined periods after the burst's peak emission. We find that the pre-peak and post-peak emission periods are statistically similar, possibly indicating a common origin. For the analyzed GRBs, we identify 24% to have more than one isolated emission episode, with 11% having at least one pre-peak event and 15% having at least one post-peak event. We identify GRB activity significantly beyond their T90, which can be important for understanding the central engine activity as well as, e.g., gravitational-wave searches.