Large-Scale Anisotropy of EGRET Gamma Ray Sources

In the course of its operation, the EGRET experiment detected high-energy -ray sources at energies above 100 MeV over the whole sky. In this communication, we search for large-scale anisotropy patterns among the catalogued EGRET sources using an expansion in spherical harmonics, accounting for EGRET’s highly non-uniform exposure. We nd signicant excess in the quadrupole and octopole moments. This is consistent with the hypothesis that, in addition to the galactic plane, a second mid-latitude ( ) population, perhaps associated with the Gould belt, contributes to the -ray ux above 100 MeV.