Supernova remnants in clumpy media: propagation of accelerated particles into clumps

International audienceSupernova remnant (SNR) shocks are sites of particle acceleration, as indicated by observationsfrom the radio to the gamma-ray domain. In particular, gamma-rays can be produced as the resultof the interaction between particles accelerated at the SNR shock and the ambient matter and/orradiation. Both protons and electrons can contribute to the observed gamma-ray emission fromSNRs, through neutral pion decay and inverse Compton scattering, respectively. Ascribing theorigin of the SNR gamma-ray emission to either hadronic or leptonic processes remains, in mostcases, an open problem, and its solution would constitute a crucial step in the quest for cosmic-ray sources. It has been proposed that the presence of dense clumps in the environment wheresupernovae explode can have a dramatic impact in shaping the hadronic gamma-ray spectrum.This is because the high-energy protons accelerated at the SNR shock are able to penetrate thedense clumps while low-energy ones cannot, and thus probe the diffuse inter-clump medium only.Here we present a numerical study of the penetration of relativistic protons into clumps which areengulfed by a SNR shock. We show that the spectrum of protons inside clumps is much harderthan that in the diffuse inter-clump medium, and we discuss the implications for the productionof hadronic gamma-rays