Multi-wavelength Emission from the Fermi Bubble II. Secondary Electrons and the Hadronic Model of the Bubble

Abstract

We analyse 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 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 loose their energy by the synchrotron and inverse-Compton, the spectrum of secondary electrons is too soft, and an additional arbitrary component of primary electrons is 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 $\propto E_e^{-2}$, the permitted range of the magnetic field strength is within 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 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 by 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 followed from observations.

arXiv comment18 pages, 4 figures. Accepted for publication in ApJ

References in corpus (20)

• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Fermi-LAT Observations of the Diffuse Gamma-Ray Emission: Implications for Cosmic Rays and the Interstellar Medium
• Parameterization of Gamma, e^+/- and Neutrino Spectra Produced by p-p Interaction in Astronomical Environment
• The Spectrum and Morphology of the Fermi Bubbles
• Microwave ISM Emission Observed by WMAP
• The Fermi Haze: A Gamma-Ray Counterpart to the Microwave Haze
• The Fermi Bubbles: Giant, Multi-Billion-Year-Old Reservoirs of Galactic Center Cosmic Rays
• Giant Magnetized Outflows from the Centre of the Milky Way
• The Fermi Bubbles: Supersonic AGN Jets with Anisotropic Cosmic Ray Diffusion
• Wild at Heart:-The Particle Astrophysics of the Galactic Centre
• Fermi gamma-ray `bubbles' from stochastic acceleration of electrons
• The gradient of diffuse gamma-ray emission in the Galaxy
• Planck Intermediate Results. IX. Detection of the Galactic haze with Planck
• The Fermi Bubbles as a Scaled-up Version of Supernova Remnants
• The Fermi Bubbles Revisited
• Magnetic substructure in the northern Fermi Bubble revealed by polarized WMAP emission
• Steady-State Hadronic Gamma-Ray Emission from 100-Myr-Old Fermi Bubbles
• Fermi bubble $\gamma$-rays as a result of diffusive injection of Galactic cosmic rays
• Multi-wavelength Emission from the Fermi Bubble I. Stochastic acceleration from Background Plasma
• Production cross sections of gamma-rays, electrons, and positrons in p-p collisions

Cited by in corpus (11)

• A Unified Model of the Fermi Bubbles, Microwave Haze, and Polarized Radio Lobes: Reverse Shocks in the Galactic Center's Giant Outflows
• The Spatially Uniform Spectrum of the Fermi Bubbles: the Leptonic AGN Jet Scenario
• Unveiling the Origin of the Fermi Bubbles
• Multi-wavelength Emission from the Fermi Bubble III. Stochastic (Fermi) Re-Acceleration of Relativistic Electrons Emitted by SNRs
• A Latitude-Dependent Analysis of the Leptonic Hypothesis for the Fermi Bubbles
• The Fermi bubbles from stochastic acceleration of electrons in a Galactic outflow
• Emission from hadronic and leptonic processes in galactic jet-driven bubbles
• The Fermi bubbles as a Superbubble
• Sources and Radiations of the Fermi Bubbles
• Multi-wavelength emission from leptonic processes in ageing galaxy bubbles
• On the high-energy protons regular acceleration in the Fermi Bubbles