The peak flux distribution of bright gamma-ray bursts measured with ULYSSES

Abstract

Observations of gamma-ray burst afterglows have shown that these events come from formidable explosions at cosmological distances. If the most distant GRBs seen by BATSE have redshifts of the order of 3-6 (e.g. GB 971214), it is a coincidence that the bright end of the GRB intensity distribution displays the -3/2 slope expected for a Euclidean distribution of sources. We analyze nearly 10 years of continuous observation of bright GRBs with {ULYSSES}, in order to constrain their intensity distribution. This extensive dataset (more than 200 bursts in the ``Euclidean'' part of the curve) is used to quantify the agreement of the data with the canonical slope of -3/2.