4.7 Article

MULTI-WAVELENGTH EMISSION FROM THE FERMI BUBBLE. II. SECONDARY ELECTRONS AND THE HADRONIC MODEL OF THE BUBBLE

Journal

ASTROPHYSICAL JOURNAL
Volume 799, Issue 1, Pages -

Publisher

IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/799/1/112

Keywords

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

Funding

  1. Government of the Hong Kong SAR [HKU 701013]
  2. LPI Educational-Scientific Complex and Dynasty Foundation
  3. RFFI [12-02-00005, 15-52-52004, 15-02-02358, 15-02-08143]
  4. Taiwan Ministry of Science and Technology [MOST 102-2112-M-008-019-MY3]
  5. International Space Science Institute

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We analyze the origin of the gamma-ray flux from the Fermi Bubbles (FBs) in the framework of the hadronic model in which gamma-rays are produced by collisions of relativistic protons with the protons of the background plasma in the Galactic halo. It is assumed in this model that the observed radio emission from the FBs is due to synchrotron radiation of secondary electrons produced by pp collisions. However, if these electrons lose their energy through synchrotron and inverse-Compton emission, the spectrum of secondary electrons will be too soft, and an additional arbitrary component of the primary electrons will be necessary in order to reproduce the radio data. Thus, a mixture of the hadronic and leptonic models is required for the observed radio flux. It was shown that if the spectrum of primary electrons is alpha E-e(-2), the permitted range of the magnetic field strength is within the 2-7 mu G region. The fraction of gamma-rays produced by pp collisions can reach about 80% of the total gamma-ray flux from the FBs. If the magnetic field is <2 mu G or >7 mu G the model is unable to reproduce the data. Alternatively, the electrons in the FBs may lose their energy through adiabatic energy losses if there is a strong plasma outflow in the GC. Then, the pure hadronic model is able to reproduce characteristics of the radio and gamma-ray flux from the FBs. However, in this case the required magnetic field strength in the FBs and the power of CR sources are much higher than those following from observations.

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