1997A&A...321..288B

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