The contribution of supernova remnants to the galactic cosmic ray spectrum

TL;DR

This paper explores how non-linear shock acceleration theory applied to supernova remnants explains the observed galactic cosmic ray spectrum, emphasizing the role of particle escape and environmental factors.

Contribution

It applies advanced non-linear acceleration theory to model cosmic ray spectra from supernova remnants, including particle escape and environmental effects.

Findings

Cosmic ray spectrum at Earth is approximately a power law with index close to -4.

The spectrum shape is sensitive to acceleration details and environmental conditions.

The model accounts for particle escape during different supernova remnant phases.

Abstract

The supernova paradigm for the origin of galactic cosmic rays has been deeply affected by the development of the non-linear theory of particle acceleration at shock waves. Here we discuss the implications of applying such theory to the calculation of the spectrum of cosmic rays at Earth as accelerated in supernova remnants and propagating in the Galaxy. The spectrum is calculated taking into account the dynamical reaction of the accelerated particles on the shock, the generation of magnetic turbulence which enhances the scattering near the shock, and the dynamical reaction of the amplified field on the plasma. Most important, the spectrum of cosmic rays at Earth is calculated taking into account the flux of particles escaping from upstream during the Sedov-Taylor phase and the adiabatically decompressed particles confined in the expanding shell and escaping at later times. We show how the spectrum obtained in this way is well described by a power law in momentum with spectral index close to -4, despite the concave shape of the instantaneous spectra of accelerated particles. On the other hand we also show how the shape of the spectrum is sensible to details of the acceleration process and environment which are and will probably remain very poorly known.