CO Observations of the Cepheus Flare. II. Gamma Rays from the Interstellar Gas and a Possible New COS B Source

Abstract

The correlation between the distribution of the interstellar gas in the Cepheus Flare region (100^deg^ <= l <= 141^deg^, 8^deg^ <= b <= 22^deg^) and that of the diffuse gamma radiation originating in these nearby clouds has been studied in detail. A maximum-likelihood analysis has been applied to compare maps of the atomic and molecular gas tracers (H I and ^12^CO observations) to the COS B γ-ray data. This yields an estimate of the 70 MeV-5 GeV emissivity spectrum of the atomic gas which agrees with previous measurements in the local interstellar medium. The results imply a value of (2.3 +/- 1.2) x 10^20^ mol cm^-2^ K^-1^ km^-1^ s for the N(H_2_)/W_CO_ ratio in the Cepheus molecular complex. The correlation study has revealed the presence of a significant (3.9 σ) pointlike excess which stands above the diffuse gamma radiation at l = 111^deg^, b = 19.8^deg^, with an error box 1.8^deg^ in radius. The excess satisfies the statistical detection criterion of the COS B catalog of sources and possibly corresponds to a new, bright, and extremely soft γ-ray source. A tentative identification could be made with the radio galaxy 3C 427.1.