Cosmic ray propagation in the interstellar magnetic fields

TL;DR

This paper explores how cosmic rays propagate through the Galaxy's magnetic fields, revealing anisotropic diffusion and small-scale anisotropies that challenge traditional diffusion models.

Contribution

It introduces explanations for observed small-scale cosmic ray anisotropies and highlights the limitations of standard diffusion assumptions in the interstellar medium.

Findings

Local magnetic field configuration causes small and medium scale anisotropies.

Cosmic rays diffuse anisotropically on scales smaller than 100 pc.

Challenges to the usual assumptions of isotropic diffusion around sources.

Abstract

The propagation of TeV-PeV cosmic rays (CR) in our Galaxy can be described as a diffusive process. We discuss here two effects, with important observational consequences, that cannot be predicted by the diffusion approximation in its usual form. First, we present an explanation for the CR anisotropies observed at small angular scales on the sky. We show that the local magnetic field configuration within a CR mean free path from Earth naturally results in CR flux anisotropies at small and medium scales. Second, we point out that TeV-PeV CRs should be expected to diffuse strongly anisotropically in the interstellar medium on scales smaller than the maximum scale of spatial fluctuations of the field, $\sim 100$ pc. This notably questions the usual assumptions on CR diffusion around sources.