Gamma-ray properties of supernova remnants transporting into molecular clouds: The cases of IC 443 and W44

Abstract

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. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.