Probing the Cosmic Star Formation History by the Brightness Distribution of Gamma‐Ray Bursts

Abstract

The brightness distribution of gamma-ray bursts (GRBs) is studied in detail under the assumption that the GRB rate is related to the cosmic star formation rate (SFR). The two populations of the long- and short-duration bursts in the 4B BATSE catalog are analyzed separately. Taking account of current uncertainties in the observational estimate of the SFR, we have tried various models of cosmic star formation history and find that the SFR evolution in z=0-1 is strongly constrained by the GRB distribution if the standard candle approximation is valid. Strong SFR evolution by a factor of ~15 from z=0 to 1, inferred from UV observations, is too steep to be consistent with the GRB distribution for any distance scale of GRBs. Some possibilities that reconcile this discrepancy are discussed, including the intrinsic luminosity dispersion of GRBs and/or the modification of star formation history estimated by UV observations. We argue that the SFR increase factor from z=0 to 1 may be as low as about 4 if we choose different sets of cosmological parameters and/or take account of the evolution of metallicity and dust extinction in the UV data, and this would significantly remedy the discrepancy.