The impact of the eROSITA bubbles on Galactic cosmic-ray transport

TL;DR

This paper suggests that Galactic outflows like the eROSITA bubbles influence cosmic-ray spectral hardening, offering an alternative to diffusion-based explanations, supported by models fitting AMS-02 data.

Contribution

It introduces a phenomenological transport model showing outflows can explain spectral hardening without additional free parameters.

Findings

Outflow boundary reproduces 300 GV spectral hardening.

Fitted outflow speed matches eROSITA outflow constraints.

Model provides an alternative to diffusion coefficient breaks.

Abstract

We propose that the observed spectral hardening in Galactic cosmic ray fluxes is governed by macroscopic Galactic outflows, such as the eROSITA bubbles, rather than microphysical variations in their scattering properties. Employing a phenomenological transport model, we show that an advective outflow boundary naturally reproduces the $300\,$GV hardening in secondary-to-primary ratios. Global fits to precision AMS-02 data yield an effective local inner halo boundary of $\sim 5\,$kpc and an outflow speed of $\sim 360\,$km/s, in striking agreement with independent multi-wavelength kinematic constraints of the eROSITA outflows. This interpretation provides a testable alternative to breaks in the effective diffusion coefficient, without increasing the number of free parameters.