Cosmic-Ray Hardenings in the Light of AMS-02

TL;DR

This paper analyzes AMS-02 cosmic ray data, revealing spectral hardening and breaks, and suggests superbubbles as the likely origin of high-rigidity Galactic cosmic rays, with implications for heavy nuclei spectra.

Contribution

It proposes that superbubbles are the primary source of high-rigidity cosmic rays, explaining spectral features and similarities among different nuclei.

Findings

Helium and carbon spectra are harder than protons by R^{0.08}.

Spectral breaks occur at R ~ 300 GV in proton and helium spectra.

CR carbon and helium spectra are similar, indicating a common origin.

Abstract

Recent precise observations of cosmic rays (CRs) by AMS-02 experiment clearly show (1) harder spectra of helium and carbon compared to protons by $\propto R^{0.08}$, and (2) concave breaks in proton and helium spectra at a rigidity $R \sim 300$ GV. In particular the helium and carbon spectra are exactly similar, pointing to the same acceleration site. We examine possible interpretations of these features and identify a chemically enriched region, that is, superbubbles as the most probable origin of Galactic CRs in high rigidity $R>30$ GV. The similar spectra of CR carbon and helium further suggest that the CRs with $R>30$ GV originate from the supernova ejecta in the superbubble core, mixed with comparable or less amount of interstellar medium. We predict similar spectra for heavy nuclei.