Do Observations Exclude Gamma-ray Bursts Originating In the Oort Cloud Of Comets?

Abstract

As long as there is no distance indicator to the sources of gamma-ray bursts all possible sources which are isotropically distributed should remain under consideration. This is why the Oort cloud of comets is kept on the list. We use the available data on the bursts' distribution of (the BATSE catalogue), and the Catalogue of Cometary Orbits by Marsden and Williams (1992) to investigate whether there is any observational indication for correlations between the angular distributions of bursts and comets' aphelia, assuming that the distribution of aphelia direction reflect, at least to some extent, true variations in the column density of the Oort cloud. We also apply the V/V_{max} test to both distributions. We have performed a variety of statistical tests (a Kolmogorov-Smirnov test for the distributions in galactic latitude, a $χ^2$ test for the spherical multiple moments, and a 2-D cross-correlation analysis), including testing sub-samples for isolating the effect of possible observational biases. These tests imply that it is unlikely that the two distributions agree, but the statistical significance is not sufficient for ruling out any connection with complete confidence. We performed Monte-Carlo simulations which show that only when the number of bursts exceeds $\sim 800$ it is possible to rule out a correlation between the angular distributions. Currently, it is only the combination of these tests with the large disagreement found for the V/V_{max} parameter which makes the Oort cloud of comets unlikely to be related to gamma-ray bursts.