LIMITS ON NUCLEAR GAMMA-RAY EMISSION FROM ORION

The discovery of gamma-ray line emission in the 3-7 MeV range from the Orion complex was recently reported. The observed Compton Telescope ( COMPTEL) spectrum suggested that the emission results from the de-exci tation of excited states of C-12 and O-16. We report on a search for t hese lines using the Oriented Scintillation Spectroscopy Experiment (O SSE) on the Compton Gamma Ray Observatory (CGRO) during a 5 week obser vation in 1995 from April to June. The OSSE detectors were pointed mid way between the Orion A and B radio sources in three different viewing configurations. We find no compelling evidence for line emission near 4.4 or 6.1 MeV. The sensitivity of the OSSE measurements is dependent on the widths of the reported C and O lines and on the source locatio n and spatial extent. A point source at the flux level reported by COM PTEL and located on-axis would have been detected by OSSE at similar t o 7 sigma and similar to 5 sigma levels of confidence for narrow and b road lines, respectively. A spatially distributed source of the same s trength with a distribution following the intense CO emission localize d around Orion A and Orion B would have been detected by OSSE at simil ar to 3.5 sigma and similar to 2.5 sigma, respectively. Thus, these OS SE observations require that any gamma-ray line source must be even mo re extended to be consistent with the reported COMPTEL intensity.