The Ep,i - Eiso correlation: type I gamma-ray bursts and the new classification method

TL;DR

This study analyzes the Ep,i - Eiso correlation in gamma-ray bursts, distinguishing between type I and II, and introduces a new classification method based on this correlation and two parameters, EH and EHD.

Contribution

The paper presents the largest sample analysis of GRB correlations and proposes a novel classification method using the Ep,i - Eiso relation and the EHD parameter.

Findings

Type I and II GRBs show distinct Ep,i - Eiso correlations.

The correlation has a similar power-law index (~0.4) for both types.

EHD is a reliable parameter for classifying GRBs without redshift data.

Abstract

We present the most extensive sample of 45 type I (short) and 275 type II (long) gamma-ray bursts (GRB) with known redshift to investigate the correlation between the rest frame peak energy, Ep,i and the total isotropic equivalent energy, Eiso of the prompt emission (Amati relation). The Ep,i - Eiso correlation for type I bursts is found to be well-distinguished from the one constructed for type II bursts and has a similar power-law index value, a = 0.4, which possibly indicates the same emission mechanism of both GRB types. We show that the initial pulse complex (IPC) of type I bursts with an extended emission and regular type I bursts follow the same correlation. We obtain similar results for type II bursts associated with Ic supernovae and for regular type II bursts. Three possible outliers from the Ep,i - Eiso correlation for type II subsample are detected. Significant evolution of the Ep,i - Eiso correlation with redshift for type II bursts is not found. We suggest the new classification method, based on the Ep,i - Eiso correlation and introduce two parameters, EH and EHD. EHD is found to be the most reliable parameter for the blind type I - type II classification, which can be used to classify GRBs with no redshift.