Resonant Particle Backscattering of a Shock Wave

TL;DR

This paper models a collisionless shock wave in the interstellar medium as a plasma instability, demonstrating how particles are backscattered and energized, contributing to cosmic ray acceleration.

Contribution

It introduces a simulation of resonant particle backscattering in shock waves, linking plasma instability parameters with particle acceleration mechanisms.

Findings

Particles bounce off the shock and become suprathermal.

Backscattered particles can be accelerated to cosmic ray energies.

The instability causes density and velocity jumps consistent with MHD theory.

Abstract

A collisionless shock wave is treated as a streaming plasma instability in the interstellar medium (ISM). We assume that in a steady state, this instability propagates through the ISM as a self-driven plasma instability, whereby the parameters of the instability are determined such that it causes density and velocity jumps as well as isotropization of the particle velocities, which then must be in accordance with MHD theory. The process of resonant interaction and particle scattering off such instability and their backscattering to an upstream region is simulated. We find that some ISM particles bounce off a shock and thus become suprathermal and eligible to enter the process of acceleration to cosmic ray energies by the mechanism of diffusive shock acceleration.