The redshift evolution of the luminosity function of type II GRBs

TL;DR

This study analyzes the evolution of the luminosity function of Type II gamma-ray bursts, finding that models with evolution fit observations better and that their luminosity function favors a broken power-law form, contrasting with long GRBs.

Contribution

It introduces a comprehensive analysis of the redshift evolution of the luminosity function for Type II GRBs using a large sample and compares different evolutionary and functional models.

Findings

No evolution model is excluded by data.

Luminosity and density evolution models fit observations well.

Type II GRBs favor a broken power-law luminosity function.

Abstract

As of December 2023, the Swift satellite has detected more than 1600 gamma-ray bursts (GRBs). We select 307 Type II GRBs for constructing the luminosity function (LF) based on the following criteria: (1) duration $T_{90} \geq 2 s$; (2) conformity with the Amati relation for Type II GRBs; and (3) peak flux $P \geq 1 \, \text{ph} \, \text{cm}^{-2} \, \text{s}^{-1}$. We explore two general forms of the GRB LF: a broken power-law (BPL) LF and a triple power-law (TPL) LF. We consider three evolutionary scenarios: no evolution, luminosity evolution, and density evolution. We find that the no evolution model can be excluded, while both luminosity and density evolution models effectively account for the observations. This result is consistent with previous studies on long GRBs (LGRBs). However, our Type II GRB sample favors a BPL LF, in contrast to the preference for a TPL function discovered in Long GRBs.