Distribution of Spectral Characteristics and the Cosmological Evolution of Gamma‐Ray Bursts

We investigate the cosmological evolution of GRBs, using the total gamma rayfluence as a measure of the burst strength. This involves an understanding ofthe distributions of the spectral parameters of GRBs as well as the totalfluence distribution - both of which are subject to detector selection effects.We present new non-parametric statistical techniques to account for theseeffects, and use these methods to estimate the true distribution of the peak ofthe nu F_nu spectrum, E_p, from the raw distribution. The distributions areobtained from four channel data and therefore are rough estimates. Here, weemphasize the methods and present qualitative results. Given its spectralparameters, we then calculate the total fluence for each burst, and compute itscumulative and differential distributions. We use these distributions toestimate the cosmological rate evolution of GRBs, for three cosmologicalmodels. Our two main conclusions are the following: 1) Given our estimates ofthe spectral parameters, we find that there may exist a significant populationof high E_p bursts that are not detected by BATSE, 2) We find a GRB co-movingrate density quite different from that of other extragalactic objects; inparticular, it is different from the recently determined star formation rate.Comment: 20 pages, including 10 postscript figures. Submitted to Ap