The Galactic Wind Haze and its $\gamma$-spectrum

TL;DR

This paper explores the gamma-ray emission in the Fermi bubbles as resulting from cosmic ray electrons with a spectrum influenced by the Galactic cosmic ray knee, suggesting a universal cosmic ray spectrum across the Galaxy.

Contribution

It proposes a model linking the gamma-ray features to the cosmic ray knee and supernovae properties, offering a unified explanation for cosmic ray spectra and gamma-ray observations.

Findings

Cosmic ray electrons steepen near 1 TeV from E^{-3} to E^{-4.2}.

The 130 GeV gamma-ray feature may be due to inverse Compton scattering.

The cosmic ray knee is consistent throughout the Galaxy.

Abstract

We study the possibility that the gamma ray emission in the Fermi bubbles observed is produced by cosmic ray electrons with a spectrum similar to Galactic cosmic rays. We argue that the cosmic ray electrons steepen near 1 TeV from $E^{-3}$ to about $E^{-4.2}$, and are partially secondaries derived from the knee-feature of normal cosmic rays. We speculate that the observed feature at $\sim 130$ GeV could essentially be due to inverse Compton emission off a pair-production peak on top of a turn-off in the $\gamma$ ray spectrum at $\sim 130$ GeV. It suggests that the knee of normal cosmic rays is the same everywhere in the Galaxy. A consequence could be that all supernovae contributing give the same cosmic ray spectrum, with the knee feature given by common stellar properties; in fact, this is consistent with the supernova theory proposed by Bisnovatyi-Kogan (1970), a magneto-rotational mechanism, if massive stars converge to common properties in terms of rotation and magnetic fields just before they explode.