Secondary Cosmic Ray Nuclei from Supernova Remnants and Constraints to the Propagation Parameters

TL;DR

This paper explores how secondary cosmic ray nuclei produced or accelerated in supernova remnants affect the determination of galactic cosmic ray propagation parameters, highlighting the importance of considering these effects in data analysis.

Contribution

It introduces a model including secondary production and re-acceleration in SNRs, showing their impact on propagation parameter estimates and emphasizing their significance for interpreting high-precision cosmic ray data.

Findings

Secondary nuclei spectra from SNRs are harder than those from ISM collisions.

Secondary-to-primary ratios flatten at ~TeV/n energies due to source effects.

Neglecting SNR contributions can misestimate the diffusion parameter delta by a factor of 5-15.

Abstract

The secondary-to-primary B/C ratio is widely used to study the cosmic ray (CR) propagation processes in the Galaxy. It is usually assumed that secondary nuclei such as Li-Be-B are entirely generated by collisions of heavier CR nuclei with the interstellar medium (ISM). We study the CR propagation under a scenario where secondary nuclei can also be produced or accelerated from galactic sources. We consider the processes of hadronic interactions inside supernova remnants (SNRs) and re-acceleration of background CRs in strong shocks. Thus, we investigate their impact in the propagation parameter determination within present and future data. The spectra of Li-Be-B nuclei emitted from SNRs are harder than those due to CR collisions with the ISM. The secondary-to-primary ratios flatten significantly at ~TeV/n energies, both from spallation and re-acceleration in the sources. The two mechanisms are complementary to each other and depend on the properties of the local ISM around the expanding remnants. The secondary production in SNRs is significant for dense background media, n ~1 cm^-3, while the amount of re-accelerated CRs is relevant for SNRs expanding into rarefied media, n ~0.1 cm-3. Due to these effects, the the diffusion parameter 'delta' may be misunderstood by a factor of ~5-15%. Our estimations indicate that an experiment of the AMS-02 caliber can constrain the key propagation parameters while breaking the source-transport degeneracy, for a wide class of B/C-consistent models. Given the precision of the data expected from on-going experiments, the SNR production/acceleration of secondary nuclei should be considered, if any, to prevent a possible mis-determination of the CR transport parameters.