Cosmic rays in the GeV-TeV energy range from two types of supernovae

TL;DR

This paper proposes a two-component model involving regular supernova remnants and Wolf-Rayet supernovae to explain the spectral differences observed in cosmic rays by AMS-02, challenging standard diffusive shock acceleration expectations.

Contribution

It introduces a novel two-component model for cosmic-ray origins that accounts for spectral variations across different species, supported by recent injection enhancement results.

Findings

The two-component model can explain the spectral differences observed by AMS-02.

Injection enhancement at supernova shocks supports the model's assumptions.

The model challenges the traditional diffusive shock acceleration theory.

Abstract

The AMS-02 experiment has reported precise measurements of energy spectra of several cosmic-ray species in the range of ~(0.5-2000) GeV/n. An intriguing finding is the differences in the spectral shape between the different species. Protons exhibit the steepest spectrum of all the species, and helium, carbon, oxygen and iron spectra are found to be harder than that of neon, magnesium and silicon. These observations are difficult to explain as diffusive shock acceleration, the currently most plausible theory for cosmic particle acceleration at high energies, expects independence of the spectral index from mass and charge of the accelerated particle. Moreover, propagation in the Galaxy has been shown to not being able to compensate for this discrepancy. In this work, we present an explanation based on two-component model for the origin of cosmic rays in the Galaxy -- the first component originating from regular supernova remnants in the interstellar medium and the second component from Wolf-Rayet supernovae. Using recent results on cosmic-ray injection enhancement at supernova shocks in the uniform interstellar medium and in the wind environment of Wolf-Rayet stars, we show that the combination of the two components may explain most of the behavior observed by the AMS-02 experiment.