Evidence for Unresolved gamma-Ray Point Sources in the Inner Galaxy

Abstract

We present a new method to characterize unresolved point sources (PSs) generalizing traditional template fits to account for non-Poissonian photon statistics. We apply this method to Fermi Large Area Telescope gamma-ray data to characterize PS populations at high latitudes and in the Inner Galaxy. We find that PSs (resolved and unresolved) account for similar to 50% of the total extragalactic gamma-ray background in the energy range similar to 1.9 to 11.9 GeV. Within 10 degrees of the Galactic Center with vertical bar b vertical bar >= 2 degrees, we find that similar to 5%-10% of the flux can be accounted for by a population of unresolved PSs distributed consistently with the observed similar to GeV gamma-ray excess in this region. The excess is fully absorbed by such a population, in preference to dark-matter annihilation. The inferred source population is dominated by near-threshold sources, which may be detectable in future searches.