Cosmic Ray Confinement and Transport Models for Probing their Putative Sources

TL;DR

This paper reviews recent models of cosmic ray confinement and transport, addressing key problems from source release to galactic propagation, aiming to enhance source identification through observational signatures.

Contribution

It introduces a Chapman-Enskog asymptotic analysis for cosmic ray transport, resolving paradoxes in diffusive propagation and exploring anisotropy phenomena.

Findings

Chapman-Enskog analysis clarifies CR diffusion paradoxes

Self-emitted Alfven waves confine CRs near sources

CR anisotropies provide clues to transport mechanisms

Abstract

Recent efforts in cosmic ray (CR) confinement and transport theory are discussed. Three problems are addressed as being crucial for understanding the present day observations and their possible telltale signs of the CR origin. The first problem concerns CR behavior right after their release from a source, such as a supernova remnant (SNR). At this phase the CRs are confined near the source by self-emitted Alfven waves. The second is the problem of diffusive propagation of CRs through the turbulent ISM. This is a seemingly straightforward and long-resolved problem, but it remains controversial and reveals paradoxes. A resolution based on the Chapman-Enskog asymptotic CR transport analysis, that also includes magnetic focusing, is suggested. The third problem is about a puzzling sharp ($\sim10^{\circ}$) anisotropies in the CR arrival directions that might bear on important clues of their transport between the source and observer. The overarching goal is to improve our understanding of all aspects of the CR's source escape and ensuing propagation through the galaxy to the level at which their sources can be identified observationally.