Non-linear diffusive acceleration of heavy nuclei in supernova remnant shocks

TL;DR

This paper presents a semi-analytical model for non-linear diffusive shock acceleration of multiple nuclei in supernova remnants, highlighting the role of magnetic field amplification and its impact on cosmic ray spectra and composition.

Contribution

It introduces a comprehensive approach that accounts for all nuclear species and magnetic field effects, advancing understanding of cosmic ray acceleration and spectral features.

Findings

Magnetic field amplification is crucial for matching observed cosmic ray spectra.

Heavier nuclei dominate the spectrum above 10^15 eV, explaining the knee feature.

Chemical composition influences gamma-ray emission from supernova remnants.

Abstract

We describe a semi-analytical approach to non-linear diffusive shock acceleration in the case in which nuclei other than protons are also accelerated. The structure of the shock is determined by the complex interplay of all nuclei, and in turn this shock structure determines the spectra of all components. The magnetic field amplification upstream is described as due to streaming instability of all nuclear species. The amplified magnetic field is then taken into account for its dynamical feedback on the shock structure as well as in terms of the induced modification of the velocity of the scattering centers that enters the particle transport equation. The spectra of accelerated particles are steep enough to be compared with observed cosmic ray spectra only if the magnetic field is sufficiently amplified and the scattering centers have high speed in the frame of the background plasma. We discuss the implications of this generalized approach on the structure of the knee in the all-particle cosmic ray spectrum, which we interpret as due to an increasingly heavier chemical composition above $10^{15}$eV. The effects of a non trivial chemical composition at the sources on the gamma ray emission from a supernova remnant when gamma rays are of hadronic origin are also discussed.