Interacting Cosmic Rays with Molecular Clouds: A Bremsstrahlung Origin of Diffuse High Energy Emission from the Inner 2deg by 1deg of the Galactic Center. (arXiv:1206.6882v1 [astro-ph.HE])

Interacting Cosmic Rays with Molecular Clouds: A Bremsstrahlung Origin of Diffuse High Energy Emission from the Inner 2deg by 1deg of the Galactic Center. (arXiv:1206.6882v1 [astro-ph.HE]):
The high energy activity in the inner few degrees of the Galactic center is
traced by diffuse radio, X-ray and gamma-ray emission. The physical
relationship between different components of diffuse gas emitting at multiple
wavelengths is a focus of this work. We first present radio continuum
observations using Green Bank Telescope and model the nonthermal spectrum in
terms of a broken power-law distribution of GeV electrons emitting synchrotron
radiation. We show that the emission detected by Fermi is primarily due to
nonthermal bremsstrahlung produced by the population of synchrotron emitting
electrons in the GeV energy range interacting with neutral gas. The
extrapolation of the electron population measured from radio data to low and
high energies can also explain the origin of FeI 6.4 keV line and diffuse TeV
emission, as observed with Suzaku, XMM-Newton, Chandra and the H.E.S.S.
observatories. The inferred physical quantities from modeling multi-wavelength
emission in the context of bremsstrahlung emission from the inner 300x120
parsecs of the Galactic center are constrained to have the cosmic ray
ionization rate 1-10x10^{-15} s^-1, molecular gas heating rate elevating the
gas temperature to 75-200K, fractional ionization of molecular gas 10^{-6} to
10^{-5}, large scale magnetic field 10-20 micro Gauss, the density of diffuse
and dense molecular gas 100 and 10^3 cm^{-3} over 300pc and 50pc pathlengths,
and the variability of FeI Kalpha 6.4 keV line emission on yearly time scales.
Important implications of our study are that GeV electrons emitting in radio
can explain the GeV gamma-rays detected by Fermi and that the cosmic ray
irradiation model, like the model of the X-ray irradiation triggered by past
activity of Sgr A*, can also explain the origin of the variable 6.4 keV
emission from Galactic center molecular clouds.