A Self-Consistent Model for the Broadband Spectrum of Sagittarius A Eastat the Galactic Center

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Abstract
Sgr A East is a very prominent elongated shell structure surrounding (although off-centered from) the Galactic nucleus. Its energetics (~4×1052 ergs), based on the power required to carve out the radio synchrotronremnant within the surrounding dense molecular cloud, appear to be extreme compared to the total energy (~1051 ergs) released in a typical supernova (SN) explosion. Yet it shares several characteristics in common with SN remnants (SNRs), the most significant of which is the ~0.1-10 GeV γ-ray spectrum measured by EGRET, if we associate the Galactic center source 2EG J1746-2852 with this nonthermal shell. We here show that the highest energy component in Sgr A East's spectrum, like that of SNRs, can be fitted with the γ-rays produced in π0 decays. Further, we demonstrate in a self-consistent manner that the leptons released in the associated π± decays produce an e± distribution that can mimic a power law with index ~3, like that inferred from the VLA data for this source. These relativistic electrons and positrons also radiate by bremsstrahlung and inverse Compton scattering with the intense IR and UV fields from the nucleus. We show that the overall emissivity calculated in this way may account for Sgr A East's broadband spectrum ranging from GHz frequencies all the way to TeV energies, where Whipple has thus far set an upper limit to the flux corresponding to a 2.5 σ signal above the noise.