Fermi bubbles from stochastic acceleration of electrons in a Galactic outflow

• 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
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201833999

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.