Qiang Yuan, Siming Liu, Xiao-Jun Bi
Supernova remnants (SNRs) are one of the most probable sources of the Galactic cosmic rays. According to the locally observed fluxes of cosmic ray protons and electrons, the electron-to-proton number ratio at the source is derived to be about 1%. Assuming such a ratio is universal for all SNRs, we propose a unified model that ascribes the distinct $\gamma$-ray spectra of different SNRs to the variation of the medium density. For the low density environment, the $\gamma$-ray emission is inverse-Compton dominated. For the high density environment like systems of high-energy particles interacting with molecular clouds, the $\gamma$-ray emission is $\pi^0$-decay dominated. This self-consistent picture can be regarded as evidence in supporting the SNR-origin of the Galactic cosmic rays.
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http://arxiv.org/abs/1203.0085
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