Revisiting the role of the streaming instability for the cosmic-ray spectrum in the GeV to TeV range

TL;DR

This paper investigates the role of streaming instability in shaping the cosmic-ray spectrum, especially the spectral hardening around 300 GeV, through revisiting and optimizing a self-consistent diffusion model.

Contribution

It revisits and refines a previous model by performing an extensive parameter study, demonstrating that self-consistent cosmic-ray transport can explain spectral hardening.

Findings

Self-consistent cosmic-ray diffusion models can explain spectral hardening.

Optimal parameters for the model fit cosmic-ray data well.

Streaming instability remains a viable explanation for spectral features.

Abstract

A complete understanding of the cosmic-ray energy spectrum remains a challenge to theory that must be met by comprehensive modeling efforts. One of these is the subject of the present study, namely, an explanation of the recently discovered spectral hardening at $\sim 300$ GeV with self-consistently treated cosmic-ray diffusion, where self-generated waves resulting from the streaming instability impact the diffusion of high-energy particles. We revisit the corresponding model by Blasi et al. (2012), perform an extensive parameter study, and determine an optimal range of parameters that best fit the cosmic-ray data. We conclude that self-consistently treated cosmic-ray transport remains a competitive alternative to explain the spectral hardening of the cosmic-ray energy spectrum at a few hundred GeV.