On the Nonthermal Emission from the Supernova Remnant W51C

TL;DR

This paper models the nonthermal emission from supernova remnant W51C, explaining radio synchrotron and gamma-ray emissions through shock acceleration and proton-proton collisions, highlighting molecular clouds as key gamma-ray sources.

Contribution

It presents a semi-analytical model linking shock acceleration processes to multiband emissions in W51C, emphasizing the role of molecular clouds in gamma-ray production.

Findings

Radio emission explained by synchrotron radiation from shock-accelerated electrons.

Gamma-rays mainly produced by proton-proton collisions in molecular clouds.

Molecular clouds can be significant sources of GeV gamma-rays in SNRs.

Abstract

The middle-aged supernova remnant (SNR) W51C is an interesting source for the interaction of the shell with a molecular cloud. The shell emits intense radio synchrotron photons, and high-energy gamma-rays from the remnant have been detected using the {\it Fermi} Large Area Telescope (LAT), the H.E.S.S. telescope, and the Milagro gamma-ray observatory. Based on a semi-analytical approach to the nonlinear shock acceleration process, we investigate the multiband nonthermal emission from W51C. The result shows that the radio emission from the remnant can be explained as synchrotron radiation of the electrons accelerated by a part of the shock flowing into the ambient medium. On the other hand, the high-energy gamma-rays detected by the {\it Fermi} LAT are mainly produced via proton-proton collisions of the high-energy protons with the ambient matter in the molecular cloud overtaken by the other part of the shock. We propose a possible explanation of the multiband nonthermal emission from W51C, and it can be concluded that a molecular cloud overtaken by a shock wave can be an important emitter in GeV $\gamma$-rays.