Galactic arm and disk plus halo models of gamma-ray burst sources

Abstract

Evidence was presented recently that at least some of the gamma‐ray burst sources are in our Galactic spiral arms. A large range of possible spiral arm spatial distributions for the gamma‐ray burst sources is investigated here, and it is shown that none of these are able to simultaneously fit the BATSE 〈V/Vmax〉, 〈cosθ〉, and 〈sin2 b〉 observations if all the sources are in the spiral arms. The current observations made by BATSE and by previous experiments are still consistent with a combined Galactic disk (or arm) plus extended Galactic halo model, provided the halo has a finite extent. A prediction of the disk plus halo model is that the fraction of the bursts observed to be in the ‘‘disk’’ population rises as the detector sensitivity improves. A careful re‐examination of the numbers of bursts in the two populations for the pre‐BATSE databases could rule out these models.