Gamma-ray Emission from Crushed Clouds in Supernova Remnants

TL;DR

This paper presents a model explaining gamma-ray and radio emissions from supernova remnants as resulting from shock-accelerated cosmic rays and compressed clouds, accounting for observed spectra and emissions.

Contribution

It introduces a model where shock compression of clouds and reacceleration of cosmic rays explain observed emissions in certain supernova remnants.

Findings

Reacceleration of pre-existing cosmic rays explains gamma-ray emission.

The model accounts for flat radio spectral indices in specific SNRs.

The gamma-ray emission is primarily from hadronic interactions in compressed clouds.

Abstract

It is shown that the radio and gamma-ray emission observed from newly-found "GeV-bright" supernova remnants (SNRs) can be explained by a model, in which a shocked cloud and shock-accelerated cosmic rays (CRs) frozen in it are simultaneously compressed by the supernova blastwave as a result of formation of a radiative cloud shock. Simple reacceleration of pre-existing CRs is generally sufficient to power the observed gamma-ray emission through the decays of neutral pions produced in hadronic interactions between high-energy protons (nuclei) and gas in the compressed-cloud layer. This model provides a natural account of the observed synchrotron radiation in SNRs W51C, W44 and IC 443 with flat radio spectral index, which can be ascribed to a combination of secondary and reaccelerated electrons and positrons.