A possible origin of gamma rays from the Fermi Bubbles

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.

arXiv comment6 pages, Talk presented at Cosmic Ray Origin- beyond the standard models, March 2014, Dolomites, Italy; published in Nuclear Physics B Proceedings

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