Gamma Ray Bursts in the Swift and GLAST Era

Abstract

We summarize our model for long-duration gamma ray bursts (GRBs) that fits the redshift (z) distributions measured with Swift and missions before Swift, and the pre-Swift GRB jet opening-angle distribution inferred from achromatic breaks in the optical light curves. We find that the comoving rate density of GRB sources exhibits positive evolution to $z \gtrsim 3$ -- 5, whereas the star formation rate inferred from measurements of the blue and UV luminosity density peaks at $z\sim 1$ -- 3. The mean intrinsic beaming factor of GRBs is found to be $\approx 34$ -- 42, and we predict that the mean GRB optical jet opening half-angle measured with Swift is $\approx 10^\circ$. We estimate the number of GRBs per year that GLAST is expected to observe based on ratios of BATSE and EGRET GRB fluences.