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

Fermi LAT has discovered two extended gamma-ray bubbles above and below the galactic plane. We propose that their origin is due to the permanent energy release in the Galactic center (GC) as a result of 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 suggest that the Bubble could generate the flux of CR protons at energies > 10¹⁵ eV because the shocks in the Bubble have much larger length scales and longer lifetime in comparison with those in SNRs. This may explain the the CR spectrum above the knee.