Magnetic field amplification by cosmic rays in supernova remnants

TL;DR

This paper investigates how cosmic rays escaping from supernova remnants can amplify magnetic fields through a non-resonant hybrid instability, with simulations showing additional density perturbations that enhance downstream magnetic amplification.

Contribution

It introduces a simulation approach representing escaping cosmic rays as a plasma return current to study magnetic field amplification in supernova remnants.

Findings

Magnetic field amplification is driven by cosmic ray-induced instabilities.

Density perturbations contribute to increased downstream amplification.

Resolution limits affect the maximum amplification achievable in simulations.

Abstract

Magnetic field amplification is needed to accelerate cosmic cays to PeV energies in supernova remants. Escaping cosmic rays trigger a return current in the plasma that drives a non-resonant hybrid instability. We run simulations in which we represent the escaping cosmic rays with the plasma return current, keeping the maximum cosmic ray energy fixed, and evaluate its effects on the upstream medium. In addition to magnetic field amplification, density perturbations arise that, when passing through the shock, further increase amplification levels downstream. As the growth rate of the instability is most rapid for the smaller scales, the resolution is a limiting factor in the amplification that can be reached with these simulations.