Statistical Evidence for Three classes of Gamma-ray Bursts

TL;DR

This study uses advanced clustering methods on the BATSE Gamma-ray burst catalog, revealing three distinct classes of GRBs with different physical properties, challenging the traditional two-class paradigm.

Contribution

It demonstrates that three classes of GRBs are statistically supported, with detailed analysis linking classes to different astrophysical origins.

Findings

Three classes of GRBs identified, instead of two.

Low and high fluence GRBs differ in energy output.

Possible links between classes and different cosmic events.

Abstract

Two different multivariate clustering techniques, the K-means partitioning method and the Dirichlet process of mixture modeling, have been applied to the BATSE Gamma-ray burst (GRB) catalog, to obtain the optimum number of coherent groups. In the standard paradigm, GRB are classified in only two groups, the long and short bursts. However, for both the clustering techniques, the optimal number of classes was found to be three, a result which is consistent with previous statistical analysis. In this classification, the long bursts are further divided into two groups which are primarily differentiated by their total fluence and duration and hence are named low and high fluence GRB. Analysis of GRB with known red-shifts and spectral parameters suggests that low fluence GRB have nearly constant isotropic energy output of 10^{52} ergs while for the high fluence ones, the energy output ranges from 10^{52} to 10^{54} ergs. It is speculated that the three kinds of GRBs reflect three different origins: mergers of neutron star systems, mergers between white dwarfs and neutron stars, and collapse of massive stars.