Cosmic rays and random magnetic traps

TL;DR

This study uses simulations to explore how magnetic traps and inhomogeneous magnetic fields influence the spatial distribution of cosmic rays in the interstellar medium, affecting radio observations and theoretical models.

Contribution

It demonstrates the impact of magnetic traps and source inhomogeneities on cosmic ray distribution, highlighting differences between protons and electrons in various magnetic configurations.

Findings

Magnetic traps cause persistent local cosmic ray inhomogeneities.

Source inhomogeneity and energy losses shape CR spatial distribution.

Protons and electrons exhibit different spatial distributions.

Abstract

The spatial distribution of cosmic ray (CR) particles in the interstellar medium (ISM) is of major importance in radio astronomy, where its knowledge is essential for the interpretation of observations, and in theoretical astrophysics, where CR contribute to the structure and dynamics of the ISM. Local inhomogeneities in interstellar magnetic field strength and structure can affect the local diffusivity and ensemble dynamics of the cosmic ray particles. Magnetic traps (regions between magnetic mirrors located on the same magnetic line) can lead to especially strong and persistent features in the CR spatial distribution. Using test particle simulations, we study the spatial distribution of an ensemble of CR particles (both protons and electrons) in various magnetic field configurations, from an idealized axisymmetric trap to those that emerge in intermittent (dynamo-generated) random magnetic fields. We demonstrate that both the inhomogeneity in the CR sources and the energy losses by the CR particles can lead to persistent local inhomogeneities in the CR distribution and that the protons and electrons have different spatial distributions. Our results can have profound implications for the interpretation of the synchrotron emission from astronomical objects, and in particular its random fluctuations.