Dr Igor Telezhinsky (Deutsches Elektronen-Synchrotron Zeuthen)
It is known that two shocks co-exist in young Supernova Remnants (SNRs) during their free expansion into the circumstellar/interstellar medium. It is widely accepted that the forward shock is responsible for the bulk of accelerated particles and the creation of a non-thermal power-law distribution of cosmic-rays. Under a test-particle approach the index of the power-law spectrum at high energies is s=2, and s<2 if non-linear theory with particle back reaction is employed. However, the observations of cosmic rays (CRs) and SNRs show that the index is typically softer, s>2. We study possible reasons for that and investigate the impact of the reverse shock on particle spectra and subsequent particle emission in young SNRs. For this purpose we use a test-particle approach to the solution of CR-transport equation and 1-D hydrodynamical simulations of SNR evolution. We found that the reverse shock significantly affects the overall distribution of high-energy particles and their emission in young SNR. Generally, the reverse shock can produce spectral features that may be mistaken as signatures of non-linear cosmic-ray feedback, and it may also be responsible for the observed softening of the high-energy emission coming from SNRs.