Non-Thermal Radio and Gamma-Ray Emissions from a Supernova Remnant by Blast Wave Breaking Out of the Circumstellar Matter

Abstract

Abstract We calculated synchrotron radio emission and $ \gamma $-ray emission due to bremsstrahlung, inverse-Compton scattering, and $ \pi ^0$-decay from the remnant of supernova that exploded in the circumstellar matter (CSM) formed by the progenitor's stellar wind. This sort of situation is a possible origin of mixed-morphology supernova remnants (SNRs), like W 49B, which exhibit recombination-radiation spectra in X-ray emission. We assumed that the CSM of 1.5 $ M_{\odot}$ exists at 0.07–3 pc away from the supernova in the interstellar medium (ISM) of density 0.016 cm$ ^{-3}$ . When the blast wave breaks out of the CSM into the ISM, its velocity rapidly increases, and hence particle acceleration is enhanced. The maximum energy of protons reaches $ \sim$ 1300 TeV just after the break-out with $ \sim$ 0.5% of the explosion energy. We considered the non-thermal emission from the blast-shocked ISM shell after the break-out. Synchrotron radio flux at 1 GHz is tens of Jy, comparable to that observed from mixed-morphology SNRs. Because of low density, the $ \gamma $-ray luminosity is dominated by inverse-Compton scattering, which is higher than the $ \pi ^0$-decay luminosity by an order of magnitude. The total $ \gamma $-ray luminosity, including bremsstrahlung, is on the order of 10$ ^{33}$ erg s$ ^{-1}$ lower than the typical value of 10$ ^{35}$ –10$ ^{36}$ erg s$ ^{-1}$ observed from mixed-morphology SNRs. However, if, e.g., $ \sim$ 10% of accelerated protons interact with some matter of density of $ \sim$ 100 cm$ ^{-3}$ , the $ \pi ^0$-decay $ \gamma $-ray luminosity would be enhanced to be comparable with the observed value.