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

Interpretation of the galactic γ-ray flux above 100 MeV has been complicated by the presence of a component due to 'point' sources of γ-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 γ-ray flux from cosmic-ray interactions with the ISM to be made for the first time. A maximum in the predicted flux is found very near the position of the COS-B source CG 78 + 1. It is proposed that the bulk of the γ-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 and good agreement is then found between the COS-B observations and predictions of both the longitude and latitude distributions of the γ-ray flux for the region 600 < l < 900. (author)