title: Fermi gamma-ray "bubbles" from stochastic acceleration of electrons.
abstract: Gamma-ray data from Fermi Large Area Telescope reveal a bilobular structure extending up to ∼50° above and below the Galactic Center. It has been argued that the gamma rays arise from hadronic interactions of high-energy cosmic rays which are advected out by a strong wind, or from inverse-Compton scattering of relativistic electrons accelerated at plasma shocks present in the bubbles. We explore the alternative possibility that the relativistic electrons are undergoing stochastic 2nd-order Fermi acceleration by plasma wave turbulence through the entire volume of the bubbles. The observed gamma-ray spectral shape is then explained naturally by the resulting hard electron spectrum modulated by inverse-Compton energy losses. Rather than a constant volume emissivity as in other models, we predict a nearly constant surface brightness, and reproduce the observed sharp edges of the bubbles.
authors.affiliation: Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3NP, United Kingdom.
authors.forename: Philipp
authors.initials: P
authors.lastname: Mertsch
authors.forename: Subir
authors.initials: S
authors.lastname: Sarkar