Plasma instabilities as a result of charge exchange in the downstream region of supernova remnant shocks

TL;DR

This paper investigates plasma instabilities caused by charge exchange in supernova remnant shocks, revealing mechanisms that amplify magnetic fields and influence shock structure, offering explanations for observed radio spectra.

Contribution

It presents a linear analysis showing how charge exchange-induced plasma instabilities can amplify magnetic fields in SNR shocks, providing an alternative to Bell's mechanism.

Findings

Resonant or Weibel instabilities dominate under typical SNR conditions.

Magnetic fields can be amplified to over 100 micro G.

The shock structure and radio spectra are affected by these instabilities.

Abstract

H-alpha emission from supernova remnants (SNRs) implies the existence of neutral hydrogen in the circumstellar medium. Some of the neutral particles penetrating the shock are ionized by the charge exchange process and make a cold ion beam in the shock downstream region. We perform linear analyses of collisionless plasma instabilities between the cold beam and the hot downstream plasma. We find that, under typical SNR conditions, either the resonant instability or the Weibel instability is the most unstable. This mechanism may amplify the magnetic field to more than 100 micro G and changes the shock structure. As a result, the radio spectrum and the large magnetic field can be explained, apart from the widely discussed Bell's mechanism.