We present a study of the high-energy diffuse emission observed toward Orion
by the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton
Gamma-Ray Observatory. The total exposure by EGRET in this region has increased
by more than a factor of two since a previous study. A simple model for the
diffuse emission adequately fits the data; no significant point sources are
detected in the region studied (l=195∘ to 220∘ and b=−25∘to−10∘) in either the composite dataset or in two separate
groups of EGRET viewing periods considered. The gamma-ray emissivity in Orion
is found to be (1.65±0.11)×10−26ssr−1 for E > 100 MeV,
and the differential emissivity is well-described as a combination of
contributions from cosmic-ray electrons and protons with approximately the
local density. The molecular mass calibrating ratio is N(H2)/WCO=(1.35±0.15)×1020cm−2(Kkm/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