Anisotropic transport and early dynamical impact of Cosmic Rays around Supernova remnants

TL;DR

This study introduces a new CR transport model in FLASH, showing how cosmic rays influence the interstellar medium around supernova remnants through anisotropic diffusion and energy-dependent effects within 150 kyr.

Contribution

It presents a novel implementation of cosmic ray physics in a magneto-hydrodynamic code, including anisotropic diffusion and spectral evolution, applied to supernova remnant environments.

Findings

CR diffusion accelerates low-density gas significantly.

Peaked CR spectra have a stronger dynamical impact than power-law spectra.

Low energy CRs distribute anisotropically with large spatial variations.

Abstract

We present a novel implementation of cosmic rays (CR) in the magneto-hydrodynamic code FLASH. CRs are described as separate fluids with different energies. CR advection, energy dependent anisotropic diffusion with respect to the magnetic field and adiabatic losses to follow the evolution of spectra are taken into account. We present a first study of the transport and immediate (~150 kyr) dynamical impact of CRs on the turbulent magnetised interstellar medium around supernova remnants on scales up to 80 pc. CR diffusion quickly leads to an efficient acceleration of low-density gas (mainly perpendicular to the magnetic field) with accelerations up to two orders of magnitude above the thermal values. Peaked (at 1 GeV) CR injection spectra have a stronger impact on the dynamics than power-law spectra. For realistic magnetic field configurations low energy CRs (with smaller diffusion coefficients) distribute anisotropically with large spatial variations of a factor of ten and more. Adiabatic losses can change the local spectra perceptibly but do not have an integral effect on the dynamics at the spatial and temporal scales considered here. We discuss the potential global impact of CRs and anisotropic transport on the dynamical structure of the ISM and also detail the limitations of the model.