Gamma-ray line emission from galaxy clusters

We report first results of a study dedicated to a search for γ-ray line emission from rich galaxy clusters, finding traces of emission from the region of Virgo and Coma near the Northern Galactic Pole (NGP). The study is based on the 6 years of COMPTEL data collected during the extended observational programme of the Compton Gamma Ray Observatory (CGRO) monitoring of the Virgo and 3C273 region. We point out the advantages of performing this study using an energy range that contains the strongest excitation γ-ray lines of 16O at 6.13, 6.9 and 7.1 MeV, as well as lines at 6.175 MeV (15O*) and 6.322 MeV (15N*) of the spallation products of the cosmic ray interactions with 16O. We discuss a generation mechanism for γ-ray line emission in merging clusters via excitation of the abundant element(s) of the intracluster matter at the merger shock by the subrelativistic protons accelerated to energies of ~10 MeV to ~100 MeV/n in the merger process.