A kinetic approach to cosmic ray induced streaming instability at supernova shocks

TL;DR

This paper develops a kinetic model to analyze cosmic ray-induced streaming instabilities at supernova shocks, revealing new insights into wave modes, their dependence on microphysics, and implications for magnetic field amplification and particle acceleration.

Contribution

It introduces a kinetic approach to study wave excitation by cosmic rays, uncovering the coexistence of resonant and non-resonant modes and their dependence on microphysical conditions.

Findings

Identification of a non-Alfvénic fast-growing mode with a dispersion relation similar to previous MHD results.

Simultaneous emergence of resonant and non-resonant modes depending on acceleration region conditions.

Implications for magnetic field amplification and particle acceleration in supernova remnants.

Abstract

We show that a purely kinetic approach to the excitation of waves by cosmic rays in the vicinity of a shock front leads to predict the appearance of a non-alfv\'enic fastly growing mode which has the same dispersion relation as that previously found by \cite{bell04} by treating the plasma in the MHD approximation. The kinetic approach allows us to investigate the dependence of the dispersion relation of these waves on the microphysics of the current which compensates the cosmic ray flow. We also show that a resonant and a non-resonant mode may appear at the same time and one of the two may become dominant on the other depending on the conditions in the acceleration region. We discuss the role of the unstable modes for magnetic field amplification and particle acceleration in supernova remnants at different stages of the remnant evolution.