MULTI-WAVELENGTH EMISSION FROM THE FERMI BUBBLE. III. STOCHASTIC (FERMI) RE-ACCELERATION OF RELATIVISTIC ELECTRONS EMITTED BY SNRs

K. S. Cheng, D. O. Chernyshov, V. A. Dogiel, C. M. Ko

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16 Scopus citations

Abstract

We analyze the model of stochastic re-acceleration of electrons that are emitted by supernova remnants (SNRs) in the Galactic Disk and then propagate into the Galactic Halo in order to explain the origin of nonthermal (radio and gamma-ray) emission from Fermi bubbles (FB). We assume that the energy for re-acceleration in the Halo is supplied by shocks generated by processes of star accretion onto the central black hole. Numerical simulations show that regions with strong turbulence (places for electron re-acceleration) are located high up in the Galactic Halo several kpc above the disk. The energy of the SNR electrons that reach these regions does not exceed several GeV due to synchrotron and inverse Compton energy losses. At appropriate parameters of re-acceleration these electrons can be re-accelerated up to an energy of 1012 eV, which explains in this model the origin of the observed radio and gamma-ray emission from the FB. However, although the model gamma-ray spectrum is consistent with the Fermi results, the model radio spectrum is steeper than that observed by WMAP and Planck. If adiabatic losses due to plasma outflows from the Galactic central regions are taken into account, then the re-acceleration model nicely reproduces the Planck data points.

Original languageEnglish
Article number135
JournalAstrophysical Journal
Volume804
Issue number2
DOIs
StatePublished - 10 May 2015

Keywords

  • Galaxy: center
  • acceleration of particles
  • gamma rays: ISM

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