A possible origin of gamma rays from the Fermi Bubbles

TL;DR

This paper explores the hypothesis that the gamma rays from the Fermi Bubbles originate from Galactic cosmic-ray protons interacting with plasma, producing gamma rays and secondary emissions observed across multiple wavelengths.

Contribution

It proposes a model where cosmic-ray protons diffusing through the Galaxy produce the observed emissions via interactions within the bubbles, offering a potential explanation for their origin.

Findings

Cosmic-ray protons can produce gamma rays through $ ext{π}^0$ decay.

Secondary electrons/positrons generate radio and microwave synchrotron emissions.

The model aligns with observed correlations across gamma-ray, radio, and X-ray data.

Abstract

One of the most exciting discoveries of recent years is a pair of gigantic gamma-ray emission regions, the so-called Fermi bubbles, above and below the Galactic center. The bubbles, discovered by the Fermi space telescope, extend up to $\sim 50^\circ$ in Galactic latitude and are $\sim 40^\circ$ wide in Galactic longitude. The gamma-ray emission is also found to correlate with radio, microwave and X-rays emission. The origin of the bubbles and the associated non-thermal emissions are still not clearly understood. Possible explanations for the non-thermal emission include cosmic-ray injection from the Galactic center by high speed Galactic winds/jets, acceleration by multiple shocks or plasma turbulence present inside the bubbles, and acceleration by strong shock waves associated with the expansion of the bubbles. In this paper, I will discuss the possibility that the gamma-ray emission is produced by the injection of Galactic cosmic-rays mainly protons during their diffusive propagation through the Galaxy. The protons interact with the bubble plasma producing $\pi^\circ$-decay gamma rays, while at the same time, radio and microwave synchrotron emissions are produced by the secondary electrons/positrons resulting from the $\pi^{\pm}$ decays.