Volume 622, February 2019
|Number of page(s)||13|
|Section||Interstellar and circumstellar matter|
|Published online||21 February 2019|
Fermi bubbles from stochastic acceleration of electrons in a Galactic outflow
Institute for Theoretical Physics and Cosmology (TTK), RWTH Aachen University,
2 Niels Bohr International Academy, Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen, Denmark
3 Kavli Institute for Particle Astrophysics & Cosmology, 2575 Sand Hill Road, M/S 29, Menlo Park, CA 94025, USA
4 Department of Physics and Applied Physics, Stanford University, Stanford, CA 94305, USA
Accepted: 7 December 2018
The discovery of the Fermi bubbles – a huge bilobular structure seen in GeV gamma-rays above and below the Galactic centre – implies the presence of a large reservoir of high energy particles at ~10 kpc from the disk. The absence of evidence for a strong shock coinciding with the edge of the bubbles, and constraints from multi-wavelength observations point towards stochastic acceleration by turbulence as a likely mechanism of acceleration. We have investigated the time-dependent acceleration of electrons in a large-scale outflow from the Galactic centre. For the first time, we present a detailed numerical solution of the particle kinetic equation that includes the acceleration, transport and relevant energy loss processes. We also take into account the addition of shock acceleration of electrons at the bubble’s blast wave. Fitting to the observed spectrum and surface brightness distribution of the bubbles allows determining the transport coefficients, thereby shedding light on the origin of the Fermi bubbles.
Key words: acceleration of particles / shock waves / turbulence / cosmic rays / ISM: jets and outflows / gamma rays: ISM
© ESO 2019
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