Cosmic-ray electron injection from the ionization of nuclei

TL;DR

This paper proposes a new electron injection mechanism at supernova remnant shocks, where ionization of heavy nuclei ejects electrons that are then accelerated, explaining observed synchrotron emissions.

Contribution

It introduces a novel electron injection process from ionization of heavy ions during acceleration, impacting cosmic ray composition and maximum energy.

Findings

Electron/proton ratio at source ~10^-4.

Ionization limits maximum energy of heavy ions.

Mechanism explains nonthermal synchrotron emission.

Abstract

We show that the secondary electrons ejected from the ionization of heavy ions can be injected into the acceleration process that occurs at supernova remnant shocks. This electron injection mechanism works since ions are ionized during the acceleration when they move already with relativistic speed, just like ejected electrons do. Using the abundances of heavy nuclei measured in cosmic rays at Earth, we estimate the electron/proton ratio at the source to be ~10^-4, big enough to account for the nonthermal synchrotron emission observed in young SNRs. We also show that the ionization process can limit the maximum energy that heavy ions can reach.