A Model of the EGRET Source at the Galactic Center:, Inverse Compton Scattering Within Sgr A East and its Halo

Fulvio Melia(1,3,4), Farhad Yusef-Zadeh(2) and Marco Fatuzzo(1)

(1)Physics Department, The University of Arizona, Tucson, AZ 85721
(2) Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208
(3) Steward Observatory, The University of Arizona, Tucson, AZ 85721
(4) Presidential Young Investigator.

Paper: ApJ, in press

EPrint Server: astro-ph/9806324


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 non-thermal particle distributions with power-law indices ~ 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 gamma -rays (2EGJ1746-2852) from within ~ 1o of the Galactic Center by EGRET onboard the Compton GRO shows that the emission from this environment extends to very high energies. We suggest that inverse Compton scatterings 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 gamma -ray source as well. We show that both particle distributions may be contributing to the gamma -ray emission, though 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 gamma -ray and hard X-ray missions.

Preprints available from the authors at melia@spacetime.physics.Arizona.EDU , or the raw TeX (no figures) if you click here.

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