The fluence distribution of gamma-ray bursts

In the use and interpretation of log N-log S distributions for gamma-ray bursts, burst peak flux has typically been used for S. We consider here the use of the fluence as a measure of S, which may be a more appropriate quantity than the peak flux in such highly variable sources. We demonstrate that the selection effects on the fluence can be determined directly from the BATSE trigger data, and then we use techniques developed elsewhere to account for the important threshold effects and correlations. Applying the appropriate corrections to the distributions, we obtain a fluence distribution that shows a somewhat sharper break than the peak flux distribution, implying a possibly narrower fluence luminosity distribution. If bursts are at cosmological distances, these observations together indicate that evolution of the luminosity function is required.