2010MNRAS.405..462F

The middle-aged supernova remnant W51C is an interesting source because of the interaction of the shell with a molecular cloud. The shell emits intense radio synchrotron photons, and high-energy γ-rays from the remnant have been detected using the Fermi Large Area Telescope (LAT), the High-Energy Stereoscopic System (H.E.S.S.) telescope, and the Milagro gamma-ray observatory. Based on a semi-analytical approach to the non-linear shock acceleration process, we investigate the multiband non-thermal emission from W51C. The result shows that the radio emission from the remnant can be explained as synchrotron radiation of the electrons accelerated by part of the shock flowing into the ambient medium. However, the high-energy γ-rays detected by the Fermi LAT are mainly produced via proton-proton collisions of the high-energy protons with the ambient matter in the molecular cloud overtaken by the other part of the shock. We propose a possible explanation for the multiband non-thermal emission from W51C. It can be concluded that a molecular cloud overtaken by a shock wave can be an important emitter in GeV γ-rays.