Gamma-ray bursts as a probe of cosmology

There is increasingly strong evidence that gamma-ray bursts (GRBs) are associated with star-forming galaxies [1,2,3,4] and occur near or in the star-forming regions of these galaxies [2,3,4,5,6]. These associations provide indirect evidence that at least the long GRBs detected by BeppoSAX are a result of the collapse of massive stars. The discovery of what appear to be supernova components in the afterglows of GRBs 970228 [7,8] and 980326 [9] provides tantalizing direct evidence that at least some GRBs are related to the deaths of massive stars, as predicted by the widely-discussed collapsar model of GRBs [10, 11,12,13,14]. If GRBs are indeed related to the collapse of massive stars, one expects the GRB rate to be approximately proportional to the star-formation rate (SFR).