The luminosity function and the rate of Swift's Gamma Ray Bursts
Abstract
We invert directly the redshift - luminosity distribution of observed long Swift GRBs to obtain their rate and luminosity function. Our best fit rate is described by a broken power law that rises like (1+z)2.1+0.5-0.6 for 0<z<3 and decrease like (1+z)-1.4+2.4-1.0 for z>3. The local rate is 1.3+0.6-0.7 [Gpc-3 yr-1]. The luminosity function is well described by a broken power law with a break at L* = 1052.5+-0.2[erg/sec] and with indices alpha = 0.2+0.2-0.1 and beta = 1.4+0.3-0.6. The recently detected GRB 090423, with redshift ~8, fits nicely into the model's prediction, verifying that we are allowed to extend our results to high redshifts. While there is a possible agreement with the star formation rate (SFR) for z<3, the high redshift slope is shallower than the steep decline in the SFR for 4<z. However we cannot rule out a GRB rate that follows one of the recent SFR models.