Can Gamma‐Ray Bursts Be Used to Measure Cosmology? A Further Analysis

Abstract

Three different methods of measuring cosmology with gamma-ray bursts (GRBs) have been proposed since a relation between the gamma-ray energy Egamma of a GRB jet and the peak energy Ep of the nu Fnu spectrum in the burst frame was reported by Ghirlanda and coauthors. In Method I, to calculate the probability for a favored cosmology, only the contribution of the Egamma-Ep relation that is already best fitted for this cosmology is considered. We apply this method to a sample of 17 GRBs, and obtain the mass density OmegaM=0.15 +0.45-0.13 ($1sigma) for a flat LambdaCDM universe. In Method II, to calculate the probability for some certain cosmology, contributions of all the possible Egamma-Ep relations that are best fitted for their corresponding cosmologies are taken into account. With this method, we find a constraint on the mass density $0.14