New COMPTEL Results on M[CLC]e[/CLC]V Gamma Rays from the Orion[solm0]Monoceros Region

Abstract

We present new COMPTEL observations of the OrionyMonoceros region, confirming our previous report of excessive 3‐7 MeV emission which we tentatively attributed to nuclear deexcitation lines at 4.44 and 6.13 MeV fromaccelerated 12 Cand 16 Onuclei.Weshowfirstresultsfromacombinationofalldataobtainedduringthefirst five years of the mission, with emphasis on the extent of the emission region. The 3‐7 MeV radiation is observed at the 9 ssignificance level with aflux of (12.8H1.5) 310 25 gcm 22 s 21 , consistent with our previousfindings. Inaddition,wecanfirmlyconcludenowthatonesinglesourcecannotexplainthemeasuredintensitydistribution: we find that the emission extends over the complex (the Orion A and B and the Mon R2 clouds), but it may actually be due to a few localized source regions. Evidence (4.4 s) for emission from the Mon OB1yOB2 area isappearingaswell.Wepresentapreliminaryspectrum(notfullydeconvolved),whichindicatesthattheemission is widely spread over the 3‐7 MeV range, suggesting a dominantly broad-line origin from energetic C and O nuclei if indeed caused by nuclear lines. The spectrum shows features that might be due to splitting of the C and O lines, but further substantiation should come from forthcoming spectral analyses and new observations. Subject headings: acceleration of particles—cosmic rays—gamma rays: observations— nuclear reactions, nucleosynthesis, abundances