Galactic Cosmic-Rays in a Breeze

TL;DR

This paper models the formation of Fermi bubbles through galactocentric outflows of gas and cosmic rays, accounting for energy losses and gamma-ray emissions, and explores their effects on cosmic-ray spectra and composition.

Contribution

It introduces a detailed model of cosmic-ray outflows in the Fermi bubbles, including energy losses and gamma-ray emission calculations, and examines their impact on cosmic-ray spectra and composition.

Findings

CR outflows produce flat gamma-ray surface brightness profiles.

Outflow profiles can cause spectral hardening of cosmic rays.

Model explains observed gamma-ray features of Fermi bubbles.

Abstract

We study a scenario in which the Fermi bubbles are formed through a Galactocentric outflow of gas and pre-accelerated cosmic-rays (CR). We take into account CR energy losses due to proton-proton interactions with the gas present in the bubbles, and calculate the associated gamma-ray emission. We find that CRs diffusing and advecting within a breeze outflow result in an approximately flat surface brightness profile of the gamma-ray emission, as observed by Fermi satellite. Finally, we apply similar outflow profiles to larger Galactocentric radii, and investigate their effects on the CR spectrum and boron-to-carbon ratio. Hardenings can appear in the spectrum, even in cases with equal CR diffusion coefficients in the disk and halo.