A New Determination of the Extragalactic Diffuse Gamma-ray Background from Egret Data

We use the GALPROP model for cosmic-ray propagation to obtain a new estimate of the Galactic component of gamma rays, and show that away from the Galactic plane it gives an accurate prediction of the observed EGRET intensities in the energy range 30 MeV – 50 GeV. On this basis we reevaluate the extragalactic gamma-ray background. We find that for some energies previous work underestimated the Galactic contribution at high latitudes and hence overestimated the background. Our new background spectrum shows a positive curvature similar to that expected for models of the extragalactic emission based on the blazar population. Subject headings: diffusion — cosmic rays — ISM: general — diffuse radiation — gamma rays: observations — gamma rays: theory