Evolution of Magnetic Fields and Cosmic Ray Acceleration in Supernova Remnants

TL;DR

This paper investigates how cosmic rays influence magnetic field amplification and polarization in supernova remnants through MHD simulations, revealing their role in explaining observed magnetic and polarization features.

Contribution

It introduces a simulation framework incorporating cosmic rays and magnetic fields to explain observed features in supernova remnants, including magnetic field strength and polarization.

Findings

Cosmic rays increase shock compression ratios significantly.

Simulations show radial magnetic field polarization consistent with observations.

Preliminary CR spectrum results align with analytical models.

Abstract

Observations show that the magnetic field in young supernova remnants (SNRs) is significantly stronger than can be expected from the compression of the circumstellar medium (CSM) by a factor of four expected for strong blast waves. Additionally, the polarization is mainly radial, which is also contrary to expectation from compression of the CSM magnetic field. Cosmic rays (CRs) may help to explain these two observed features. They can increase the compression ratio to factors well over those of regular strong shocks by adding a relativistic plasma component to the pressure, and by draining the shock of energy when CRs escape from the region. The higher compression ratio will also allow for the contact discontinuity, which is subject to the Rayleigh-Taylor (R-T) instability, to reach much further out to the forward shock. This could create a preferred radial polarization of the magnetic field. With an adaptive mesh refinement MHD code (AMRVAC), we simulate the evolution of SNRs with three different configurations of the initial CSM magnetic field, and look at two different equations of state in order to look at the possible influence of a CR plasma component. The spectrum of CRs can be simulated using test particles, of which we also show some preliminary results that agree well with available analytical solutions.