2013MNRAS.435..570F

Motivated by the recent report of the detailed spectra of IC 443 and W44 based on four years of observations with the Fermi Large Area Telescope, γ-rays produced via proton-proton interaction in the two supernova remnants (SNRs) have been investigated in the diffusive shock acceleration scenario. In the model, a part of the SNR shell transporting into ambient dense molecular clouds (MCs), and a shock with a relatively low Alfvén Mach number can be produced. Relativistic protons are accelerated in the shock via the diffusive acceleration process; moreover, a break in the particle distribution is induced since the damping of Alfvén waves when the shock transporting into partly ionized plasma. A spectrum of the accelerated protons in the shock can be obtained in the test-particle case, taking into account the effect of the ambient partly ionized plasma on the acceleration process. Furthermore, hadronic γ-rays with a peak around severalGeVs are reproduced as the protons inelastically colliding with the ambient matter of the crushed gas. The observed γ-ray spectral distributions of the SNR IC 443 and W44 can be successfully reproduced using the static model in the test-particle scenario. It can be concluded that the observed γ-rays can be explained in the diffusive shock case as the shock waves transporting into the dense MCs for the two remnants.