COMPTEL DETECTION OF LOW-ENERGY GAMMA-RAYS FROM THE HVC COMPLEX-M ANDCOMPLEX-A REGION

We report the first observational indication for extended MeV emission that may be associated with high-velocity clouds (HVCs). Based on a c ombination of fifteen COMPTEL observations made during the period 1991 -1995 we find evidence for intense gamma-radiation at 0.75-3 MeV from the general direction of the HVC Complexes M and A, adjacent to the Lo ckman et al. hole. The gamma-ray excess roughly covers a region of exc eptionally low HI column densities and appears to consist of a time-va riable source and persistent, likely diffuse, emission. The (enhanced) diffuse soft X-rays from this HVC area seen by ROSAT may be closely r elated to the gamma-ray emission. We show that the X-ray and gamma-ray emission can both be attributed to nonthermal electron bremsstrahlung arising from HVC interactions with the galactic disk or lower halo.