Supernova remnants in molecular clouds: on cosmic ray electron spectra

TL;DR

This paper explores how shock wave acceleration, combined with turbulence-induced second-order Fermi acceleration, can explain the flat synchrotron spectra observed in supernova remnants within molecular clouds.

Contribution

It proposes a new explanation involving combined acceleration processes for the spectral features of SNRs in molecular clouds.

Findings

Medium Alfvén Mach number shocks can produce the observed spectral indices.

Second-order Fermi acceleration contributes significantly to particle energization.

The model aligns with observed flat synchrotron spectra in SNRs.

Abstract

The particle acceleration process at a shock wave, in the presence of the second-order Fermi acceleration in the turbulent medium near the shock, is discussed as an alternative explanation for the observed flat synchrotron spectra of supernova remnants (SNRs) in molecular clouds. We argue that medium Alfv\'en Mach number shocks considered by Chevalier (1999, ApJ, in press) for such SNRs can naturally lead to the observed spectral indices.