The duration distribution of Swift Gamma-Ray Bursts

TL;DR

This study analyzes the duration distribution of 888 Swift gamma-ray bursts, confirming three distinct groups with statistical significance and examining their redshift distributions, revealing differences especially for short bursts.

Contribution

It provides a detailed statistical analysis confirming three gamma-ray burst classes using a large Swift dataset and examines their redshift distributions, clarifying previous ambiguities.

Findings

Three distinct GRB duration groups confirmed with high significance.

Redshift distribution differs notably for short GRBs compared to other groups.

No evidence found for a fourth GRB duration component.

Abstract

Decades ago two classes of gamma-ray bursts were identified and delineated as having durations shorter and longer than about 2 s. Subsequently indications also supported the existence of a third class. Using maximum likelihood estimation we analyze the duration distribution of 888 Swift BAT bursts observed before October 2015. Fitting three log-normal functions to the duration distribution of the bursts provides a better fit than two log-normal distributions, with 99.9999% significance. Similarly to earlier results, we found that a fourth component is not needed. The relative frequencies of the distribution of the groups are 8% for short, 35% for intermediate and 57% for long bursts which correspond to our previous results. We analyse the redshift distribution for the 269 GRBs of the 888 GRBs with known redshift. We find no evidence for the previously suggested difference between the long and intermediate GRBs' redshift distribution. The observed redshift distribution of the 20 short GRBs differs with high significance from the distributions of the other groups.