Limit on the average redshift of Gamma Ray Bursts from evolving galaxies

Abstract

Identification of gravitationally lensed Gamma Ray Bursts (GRBs) in the BATSE 4B catalog can be used to constrain the average redshift <z> of the GRBs. Here we calculate an upper limit to <z>, independent of the physical model for GRBs, using a filled beam approximation to compute the lensing rate for GRBs at high z for a variety of cosmologies. The upper limit on <z> depends directly on the cosmological parameters ? and ?. The other factor which can change the <z> of GRBs is the evolution of the lensing galaxies. We find that merging of lensing galaxies puts the GRBs at higher redshift as compare to non evolving model of galaxies.