Particle acceleration and the origin of gamma-ray emission from Fermi Bubbles

TL;DR

This paper proposes that the Fermi Bubbles' gamma-ray emission results from shock-accelerated electrons and protons, originating from quasi-periodic star accretion events in the Galactic center, explaining high-energy cosmic rays.

Contribution

It introduces a novel model linking star accretion-induced shocks to particle acceleration and gamma-ray emission in the Fermi Bubbles, explaining their origin and cosmic ray spectrum above the knee.

Findings

Electrons up to ~10 TeV can produce observed gamma rays via inverse Compton scattering.

Shocks in the Bubbles can generate cosmic ray protons above 10^15 eV.

The model links Galactic center activity to high-energy phenomena in the halo.

Abstract

Fermi LAT has discovered two extended gamma-ray bubbles above and below the galactic plane. We propose that their origin is due to the energy release in the Galactic center (GC) as a result of quasi-periodic star accretion onto the central black hole. Shocks generated by these processes propagate into the Galactic halo and accelerate particles there. We show that electrons accelerated up to ~10 TeV may be responsible for the observed gamma-ray emission of the bubbles as a result of inverse Compton (IC) scattering on the relic photons. We also suggest that the Bubble could generate the flux of CR protons at energies > 10^15 eV because the shocks in the Bubble have much larger length scales and longer lifetimes in comparison with those in SNRs. This may explain the the CR spectrum above the knee.