On the cosmic ray spectrum from type II Supernovae

TL;DR

This paper explores how non-resonant streaming instability in type II supernovae can accelerate cosmic rays to PeV energies, but faces challenges in simultaneously explaining different observational data sets.

Contribution

It introduces a model of cosmic ray acceleration in type II supernovae using non-resonant instability, highlighting its potential to reach PeV energies and analyzing its limitations.

Findings

Maximum proton energy can reach PeV levels.

Spectral break occurs at the maximum energy without a high-energy exponential cutoff.

The model cannot simultaneously fit KASCADE Grande and ARGO-YBJ data.

Abstract

One of the most important challenges for the largely accepted idea that Galactic CRs are accelerated in SNR shocks is the maximum energy at which particles can be accelerated. The resonant streaming instability, long invoked for magnetic field amplification at shocks, can not provide sufficiently high fields and efficient enough scattering so as to ensure particle acceleration up to the knee. Here we discuss the non-resonant version of this instability which, with its faster growth and larger value of the amplified field, increases the achievable maximum energy. Because of their higher explosion rate, we focus on type II SNe expanding in their red supergiant wind and we find that the transition between Ejecta Dominated (ED) and Sedov-Taylor (ST) phases takes place at very early times. In this environment, the accelerated particle spectrum shows no high energy exponential cut-off but a spectral break at the maximum energy (EM). Moreover, the maximum energy of protons can easily reach PeV energies. With this model, we tried to fit KASCADE Grande and ARGO -YBJ data but failed to find a parameter combination that can explain both data sets. We discuss the different scenarios implied by the two data sets.