30TH INTERNATIONAL COSMIC RAY CONFERENCE Hadronic gamma rays from supernova remnants

Abstract: A gas cloud near a supernova remnant (SNR) provides a target for pp-collisions leading to subsequent γ-ray emission through pi0-decay. The assumption of a power-law ambient spectrum of accelerated particles with index near –2 is usually built into models predicting the spectra of very-high energy (VHE) γ-ray emission from SNRs. However, if the gas cloud is located at some distance from the SNR shock, this assumption is not necessarily correct. In this case, the particles which interact with the cloud are those leaking from the shock and their spectrum is approximately monoenergetic with the injection energy gradually decreasing as the SNR ages. The γ-ray spectrum resulting from particle interactions with the gas cloud will be flatter than expected, with the cutoff defined by the pion momentum distribution in the laboratory frame. We evaluate the flux of particles escaping from a SNR shock and apply the results to the VHE diffuse emission detected by the HESS at the Galactic centre