COMPTEL observations of the Orion complex: evidence for cosmic-ray induces gamma-ray lines

Abstract

We report the detection of gamma-ray emission from the Orion complex in the 3-7 MeV range by the COMPTEL telescope aboard the Compton Gamma Ray Observatory. This emission can be identified with the 4.44 MeV and 6.13 MeV nuclear de-excitation lines of C-12* and O-16*, respectively, which are predicted to be the strongest gamma-ray lines originating from the interaction of energetic particles with ambient matter. However, the observed flux of (1.0 +/- 0.15) X 10(-4) photon cm-2 s-1 (3-7 MeV) is much larger than anticipated. There is good circumstantial evidence that our findings indicate strongly enhanced abundances of C and O in low-energy cosmic rays (approximately 10 MeV/nucleon), rather than high fluxes of cosmic-ray protons and alpha-particles. The positrons resulting from energetic particle interactions in the Orion region should produce 511 keV annihilation radiation that is detectable by OSSE.</p