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 \lower 2.15 pt \hbox { $ \buildrel > \over { \sim } $ } 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 .