Grammage of cosmic rays in the proximity of supernova remnants embedded in a partially ionized medium

TL;DR

This study examines how damping mechanisms in partially ionized media near supernova remnants limit cosmic ray confinement, showing that local grammage accumulation is negligible, supporting the standard galactic cosmic ray propagation model.

Contribution

It provides a detailed analysis of damping effects on cosmic ray confinement near sources, demonstrating that these effects do not significantly alter the overall grammage accumulated in the galaxy.

Findings

Ion-neutral and turbulent damping limit cosmic ray residence time near sources.

Grammage accumulated near sources is negligible due to damping effects.

Standard galactic cosmic ray propagation models remain valid.

Abstract

We investigate the damping of Alfv\'en waves generated by the cosmic ray resonant streaming instability in the context of the cosmic ray escape and propagation in the proximity of supernova remnants. We consider ion-neutral damping, turbulent damping and non linear Landau damping in the warm ionized and warm neutral phases of the interstellar medium. For the ion-neutral damping, up-to-date damping coefficients are used. We investigate in particular whether the self-confinement of cosmic rays nearby sources can appreciably affect the grammage. We show that the ion-neutral damping and the turbulent damping effectively limit the residence time of cosmic rays in the source proximity, so that the grammage accumulated near sources is found to be negligible. Contrary to previous results, this also happens in the most extreme scenario where ion-neutral damping is less effective, namely in a medium with only neutral helium and fully ionized hydrogen. Therefore, the standard picture, in which CR secondaries are produced during the whole time spent by cosmic rays throughout the Galactic disk, need not to be deeply revisited.