Cosmological Evolution of Long Gamma-ray Bursts and Star Formation Rate

TL;DR

This study uses a non-parametric method to analyze a large sample of long gamma-ray bursts, revealing their luminosity evolution, a broken power-law luminosity function, and a star formation rate that exceeds the SFR at low redshifts, providing insights into early universe conditions.

Contribution

It introduces the use of Efron Petrosian methods for non-parametric analysis of GRB characteristics and their evolution, offering a new approach compared to traditional forward fitting techniques.

Findings

Strong luminosity evolution observed.

Luminosity function fits a broken power law.

High formation rate at low redshifts exceeds SFR.

Abstract

Gamma-ray bursts (GRBs) by virtue of their high luminosities can be detected up to very high redshifts and therefore can be excellent probes of the early universe. This task is hampered by the fact that most of their characteristics have a broad range so that we first need to obtain an accurate description of the distribution of these characteristics, and specially, their cosmological evolution. We use a sample of about 200 \swift long GRBs with known redshift to determine the luminosity and formation rate evolutions and the general shape of the luminosity function. In contrast to most other forward fitting methods of treating this problem we use the Efron Petrosian methods which allow a non-parametric determination of above quantities. We find a relatively strong luminosity evolution, a luminosity function that can be fitted to a broken power law, and an unusually high rate of formation rate at low redshifts, a rate more than one order of magnitude higher than the star formation rate (SFR). On the other hand, our results seem to agree with the almost constant SFR in redshifts 1 to 3 and the decline above this redshift.