Abstract
We present new COMPTEL observations of the Orion/Monoceros 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 from accelerated 12C and 16O nuclei. We show first results from a combination of all data obtained during the first five years of the mission, with emphasis on the extent of the emission region. The 3-7 MeV radiation is observed at the 9 σ significance level with a flux of (12.8 ± 1.5) × 10-5 γ cm-2 s-1, consistent with our previous findings. In addition, we can firmly conclude now that one single source cannot explain the measured intensity distribution: 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 σ) for emission from the Mon OB1/OB2 area is appearing as well. We present a preliminary spectrum (not fully deconvolved), which indicates that the emission 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.
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