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.
