Turbulent magnetic field amplification driven by cosmic-ray pressure gradients

TL;DR

This paper introduces a model where cosmic-ray pressure gradients induce turbulence in the inhomogeneous ISM, significantly amplifying magnetic fields near supernova remnants, aligning with observational data.

Contribution

The study presents a simple, effective model demonstrating magnetic field amplification via turbulence driven by cosmic-ray pressure gradients in the ISM.

Findings

Magnetic fields can be amplified by factors of 20 or more.

Turbulence is generated through differential acceleration of the ISM.

Amplification occurs over the diffusion length of high-energy particles.

Abstract

Observations of non-thermal emission from several supernova remnants suggest that magnetic fields close to the blastwave are much stronger than would be naively expected from simple shock compression of the field permeating the interstellar medium (ISM). We present a simple model which is capable of achieving sufficient magnetic field amplification to explain the observations. We propose that the cosmic-ray pressure gradient acting on the inhomogeneous ISM upstream of the supernova blastwave induces strong turbulence upstream of the supernova blastwave. The turbulence is generated through the differential acceleration of the upstream ISM which occurs as a result of density inhomogeneities in the ISM. This turbulence then amplifies the pre-existing magnetic field. Numerical simulations are presented which demonstrate that amplification factors of 20 or more are easily achievable by this mechanism when reasonable parameters for the ISM and supernova blastwave are assumed. The length scale over which this amplification occurs is that of the diffusion length of the highest energy non-thermal particles.