Gamma-Ray Bursts and the Cosmic Star Formation Rate

We have tested several models of GRB luminosity and redshift distribution functions for compatibility with the BATSE 4B number versus peak flux relation. Our results disagree with recent claims that current GRB observations can be used to strongly constrain the cosmic star formation history. Instead, we find that relaxing the assumption that GRBs are standard candles renders a very broad range of models consistent with the BATSE number-flux relation. We explicitly construct two sample distributions, one tracing the star formation history and one with a constant comoving density. We show that both distributions are compatible with the observed fluxes and redshifts of the bursts GRB970508, GRB971214, and GRB980703, and we discuss the measurements required to distinguish the two models.