THE SPATIAL-DISTRIBUTION OF GAMMA-RAY BURSTS FROM PIONEER-VENUS-ORBITER

A sample of 225 observed gamma-ray bursts between 1978 September and 1988 July from the Pioneer Venus Orbiter (PVO) has been recently studied to test the homogeneity of the burst source population in space with the log N(> P(c))-log P(c) and log (dN/dP(c))-log P(c) relations. The N(> P(c)) is the number of bursts yr-1 which have maximum photon count rates in excess of P(c), dN/dP(c) is the number of bursts yr-1 (counts [0.25 s]-1)-1, and P(c) is the peak count rate (counts [0.25 s]-1) above the background. The relations N(> P(c)) approximately P(c)-1.5 and dN/dP(c) approximately P(c)-2.5 are expected if the gamma bursters are uniformly distributed in space. The Kolmogorov-Smirnov statistic gives a probability of 0.93 that the observed integral distribution N(> P(c)) is drawn from the expected uniform distribution P(c)-1.5. A least-squares 1 standard deviation fit to the observed differential distribution gives dN/dP(c) approximately P(c)-2.42 +/- 0.07. Both are consistent with a uniform distribution in space of the parent population of burst sources. The differential fit was possible, for the first time, because of the large number of events in the PVO data set.