2004ApJ...617L.123A

The HESS (High Energy Stereoscopic System) collaboration recently reported highly significant detection of TeV γ-rays coincident with Sgr A*. In the context of other Galactic center (GC) observations, this points to the following scenario: In the extreme advection-dominated accretion flow (ADAF) regime of the GC black hole (BH), synchrotron radio/submillimeter emission of ∼100 MeV electrons emanates from an inefficiently radiating turbulent magnetized corona within 20R_S(Schwarzschild radii) of the GCBH. These electrons are accelerated through second-order Fermi processes by MHD turbulence, as suggested by Liu et al. Closer to the innermost stable orbit of the ADAF, instabilities and shocks within the flow inject power-law electrons through first-order Fermi acceleration to make synchrotron X-ray flares observed with Chandra, XMM, and INTEGRAL. A subrelativistic MHD wind subtending an ∼1 sr cone with power ≳10³⁷ ergs/s is driven by the ADAF from the vicinity of the GCBH. As in pulsar-powered plerions, electrons are accelerated at the wind termination shock at ≳10^16.5 cm from the GCBH, and Compton-scatter the ADAF and the far-infrared dust radiation to TeV energies. The synchrotron radiation of these electrons forms the quiescent X-ray source resolved by Chandra. The radio counterpart of this TeV/X-ray plerion, formed when the injected electrons cool on timescales of ≳10⁴ yr, could explain the origin of nonthermal radio emission in the parsec-scale bar of the radio nebula Sgr A West.