Supernova remnants in clumpy media: propagation of accelerated particles into clumps
August 30, 2017
August 03, 2018
Supernova remnant (SNR) shocks are sites of particle acceleration, as indicated by observations
from the radio to the gamma-ray domain. In particular, gamma-rays can be produced as the result
of the interaction between particles accelerated at the SNR shock and the ambient matter and/or
radiation. Both protons and electrons can contribute to the observed gamma-ray emission from
SNRs, through neutral pion decay and inverse Compton scattering, respectively. Ascribing the
origin of the SNR gamma-ray emission to either hadronic or leptonic processes remains, in most
cases, 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 where
supernovae 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 the
dense 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 are
engulfed by a SNR shock. We show that the spectrum of protons inside clumps is much harder
than that in the diffuse inter-clump medium, and we discuss the implications for the production
of hadronic gamma-rays.
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