A model of the EGRET source at the Galactic Center: inverse Compton scattering within Sagittarius A East and its halo.
MELIA F., YUSEF-ZADEH F. and FATUZZO M.
Abstract (from CDS):
Continuum low-frequency radio observations of the Galactic center reveal the presence of two prominent radio sources, Sgr A East and its surrounding halo, containing nonthermal particle distributions with power-law indexes ∼2.5-3.3 and ∼2.4, respectively. The central 1-2 pc region is also a source of intense (stellar) UV and (dust-reprocessed) far-IR radiation that bathes these extended synchrotron-emitting structures. A recent detection of γ-rays (2EG J1746-2852) from within ∼1° of the Galactic center by EGRET onboard the ComptonGammaRayObservatory (CGRO) shows that the emission from this environment extends to very high energies. We suggest that inverse Compton scattering between the power-law electrons inferred from the radio properties of Sgr A East and its halo and the UV and IR photons from the nucleus may account for the possibly diffuse γ-ray source as well. We show that both particle distributions may be contributing to the γ-ray emission, although their relevant strength depends on the actual physical properties (such as the magnetic field intensity) in each source. If this picture is correct, the high-energy source at the Galactic center is extended over several arcminutes, which can be tested with the next generation of γ-ray and hard X-ray missions.
Acceleration of Particles - Black Hole Physics - Galaxy: Center - Galaxies: Nuclei - Gamma Rays: Theory - Radiation Mechanisms: Nonthermal