Fermi bubbles from stochastic acceleration of electrons in a Galactic outflow

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...

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Bibliographic Details
Published in:Astronomy and astrophysics (Berlin) 2019-02, Vol.622, p.A203
Main Authors: Mertsch, P., Petrosian, V.
Format: Article
Language:English
Subjects:
Acceleration
acceleration of particles
Brightness distribution
Bubbles
cosmic rays
Electrons
Energy dissipation
Energy loss
gamma rays: ISM
ISM gamma rays
ISM jets and outflows
Kinetic equations
Outflow
PARTICLE ACCELERATORS
shock waves
Surface brightness
Time dependence
Transport properties
Turbulence
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Summary: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.
ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361/201833999