Indications for Gamma-Ray Bursts Originating within an Extended Galactic Halo ?

Abstract

If a substantial fraction of the observed gamma-ray bursts originates within an extended Galactic halo then their spatial distribution should deviate slightly from spherical symmetry in a very particular way which involves features both in the bursts' angular and radial distributions. This conclusion is based on various reasons which are all related to the presence and motion of the satellite galaxies around the Galaxy, and is independent of the nature and origin of the sources. We analyze the spatial distribution of the bursts, according to the BATSE catalog until March 1992, and argue that the expected signature of an extended Galactic halo model is indicated by the data. The distance to the faintest bursts in the halo is either $\sim130$ Kpc or $\sim270$ Kpc. Although a signature of a nearby-extragalactic distance scale in the data is very suggestive, we argue that a comparison with specific models is necessary before regarding our findings as a conclusive evidence. If the increasing data supports our results then gamma-ray bursts may be the first detected manifestations of nearby intergalactic objects, either primordial or which have escaped predominantely from our satellite galaxies.