Evaluation of Models for Diffuse Continuum Gamma Rays in EGRET Range

Abstract

The GALPROP model for cosmic-ray propagation produces explicit predictions for the angular distribution of gamma-rays. We compare our current models with EGRET spectra for various regions of the sky. This allows a critical test of alternative hypotheses for the observed GeV excess. We show that a population of hard-spectrum sources cannot be solely responsible for the excess since it also appears at high latitudes; on the other hand the 'hard electron' spectrum model cannot explain the gamma-ray excess in the inner Galaxy. Hence some combination of these explanations is required.