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.
- Publication:
-
Physical Review Letters
- Pub Date:
- August 2011
- DOI:
- 10.1103/PhysRevLett.107.091101
- arXiv:
- arXiv:1104.3585
- Bibcode:
- 2011PhRvL.107i1101M
- Keywords:
-
- 98.70.Rz;
- 95.30.Qd;
- 98.35.Jk;
- 98.70.Sa;
- gamma-ray sources;
- gamma-ray bursts;
- Magnetohydrodynamics and plasmas;
- Galactic center bar circumnuclear matter and bulge;
- Cosmic rays;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Cosmology and Extragalactic Astrophysics;
- Astrophysics - Galaxy Astrophysics
- E-Print:
- 4 pages, 4 figures