Gamma rays from the Cygnus region and the nature of CG 78+1.

Interpretation of the galactic gamma-ray flux above 100 MeV has been complicated by the presence of a component due to 'point' sources of gamma-rays and by the lack of measurements of the molecular hydrogen (except along the galactic equator) which forms a large fraction of the interstellar medium (ISM). Recent CO observations of the Cygnus X region by the Columbia group have enabled reliable predictions of the gamma-ray flux from cosmic-ray interactions with the ISM to be made for the first time. A maximum in the predicted flux very near the position of the COS-B source CG 78 + 1 is found. It is proposed that the bulk of the gamma-ray flux in the vicinity of CG 78 + 1 is a consequence of interactions of cosmic rays with the gas in the cloud complexes in the Cygnus X region. The COS-B observations and predictions of both the longitude and latitude distributions of the gamma-ray flux for the region between 60 and 90 deg were found to agree well.