Search for Cosmological time dilation from Gamma-Ray Bursts -- A 2021 status update

TL;DR

This study investigates whether gamma-ray burst light curves exhibit cosmological time dilation effects by analyzing durations across a large sample, finding some evidence consistent with the expected dilation, especially in binned data.

Contribution

It provides a comprehensive analysis of GRB durations for cosmological time dilation, including new methods and publicly available analysis code.

Findings

Weighted mean-based binned data supports time dilation signature.

Unbinned data shows large scatter, less conclusive.

Analysis codes and procedures are publicly released.

Abstract

We carry out a search for signatures of cosmological time dilation in the light curves of Gamma Ray Bursts (GRBs), detected by the Neil Gehrels Swift Observatory. For this purpose, we calculate two different durations ($T_{50}$ and $T_{90}$) for a sample of 247 GRBs in the fixed rest frame energy interval of 140-350 keV, similar to Zhang et al. We then carry out a power law-based regression analysis between the durations and redshifts. This search is done using both the unbinned as well as the binned data, where both the weighted mean and the geometric mean was used. For each analysis, we also calculate the intrinsic scatter to determine the tightness of the relation. We find that weighted mean-based binned data for long GRBs and the geometric mean-based binned data is consistent with the cosmological time dilation signature, whereas the analyses using unbinned durations show a very large scatter. We also make our analysis codes and the procedure for obtaining the light curves and estimation of $T_{50}$/$T_{90}$ publicly available.