Hybrid origins of the cosmic-ray nuclei spectral hardening at a few hundred GV

TL;DR

This paper investigates the spectral hardening of cosmic-ray nuclei at a few hundred GV, demonstrating that it results from a combination of propagation effects and source superposition, with evidence from AMS-02 data analysis.

Contribution

It provides a comprehensive analysis showing that both diffusion coefficient breaks and source injection spectrum breaks are necessary to explain the spectral hardening, indicating hybrid origins.

Findings

Both diffusion and source spectrum breaks are needed for modeling.

CR spectral indices of He and Ne differ at low rigidity, suggesting different origins.

Spectral hardening is due to multiple contributing factors.

Abstract

Many experiments have confirmed the spectral hardening at a few hundred GV of cosmic-ray (CR) nuclei spectra, and three general different origins have been proposed: the primary source acceleration, the propagation, and the superposition of different kinds of sources. The AMS-02 CR nuclei spectra of He, C, N, O, Ne, Mg, Si, and B (which including B and its dominating parents species) are collected to study the necessity of employing a break in diffusion coefficient and independent breaks in primary source injection spectra to reproduce the spectral hardening at a few hundred GV. For comparison, three different schemes are introduced to do the global fitting. The fitting results show that both the break in diffusion coefficient and the independent breaks in primary source injection spectra are needed, which are corresponding to the spatial dependent propagation and the superposition of different kinds of sources, respectively. Consequently, the nuclei spectral hardening in a few hundred GV should have hybrid origins. Moreover, the CR spectral indices of He and Ne show large deviations to other species in low-rigidity region, which indicates their different CR origins.