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

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 (T50 and T90) for a sample of 247 GRBs in the fixed rest frame energy interval of 140-350 keV, similar to a previous work [1]. 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 T50/T90 publicly available.

Search for Lorentz invariance violation using Bayesian model comparison applied to Xiao et al. GRB spectral lag catalog

“…GRBs are single-shot explosions located at cosmological distances, which were first detected in 1960s and have been observed over 10 decades in energies from keV to over 10 TeV range [28], with the maximum GRB energy equal to 18 TeV [29]. They are located at cosmological distances, although a distinct time-dilation signature in the light curves is yet to be seen [30]. GRBs are traditionally divided into two categories based on their durations, with long (short) GRBs lasting more (less) than two seconds [31].…”