EGRET Observations of the Diffuse Gamma‐Ray Emission in Orion: Analysis through Cycle 6

We present a study of the high-energy diffuse emission observed toward Orionby the Energetic Gamma-Ray Experiment Telescope (EGRET) on the ComptonGamma-Ray Observatory. The total exposure by EGRET in this region has increasedby more than a factor of two since a previous study. A simple model for thediffuse emission adequately fits the data; no significant point sources aredetected in the region studied ($l = 195^\circ$ to $220^\circ$ and $b =-25^\circ to -10^\circ$) in either the composite dataset or in two separategroups of EGRET viewing periods considered. The gamma-ray emissivity in Orionis found to be $(1.65 \pm 0.11) \times 10^{-26} {s sr}^{-1}$ for E > 100 MeV,and the differential emissivity is well-described as a combination ofcontributions from cosmic-ray electrons and protons with approximately thelocal density. The molecular mass calibrating ratio is $N(H_2)/W_{CO} = (1.35\pm 0.15) \times 10^{20} cm^{-2} (K km/s)^{-1}$.Comment: 16 pages, including 5 figures. 3 Tables as three separate files. Latex document, needs AASTEX style files. Accepted for publication in Ap