  The recent detection of a three-hour X-ray flare from Sgr A* by Chandra
provides very strong evidence for a compact emitting region near this
supermassive black hole at the Galactic center. Sgr A*'s mm/sub-mm spectrum and
polarimetric properties, and its quiescent-state X-ray flux density, are
consistent with a model in which low angular momentum gas captured at large
radii circularizes to form a hot, magnetized Keplerian flow within tens of
Schwarzschild radii of the black hole's event horizon. In Sgr A*'s quiescent
state, the X-ray emission appears to be produced by self-Comptonization (SSC)
of the mm/sub-mm synchrotron photons emitted in this region. In this paper, we
show that the prominent X-ray flare seen in Sgr A* may be due to a sudden
enhancement of accretion through the circularized flow. Depending on whether
the associated response of the anomalous viscosity is to increase or decrease
in tandem with this additional injection of mass, the X-ray photons during the
outburst may be produced either via thermal bremsstrahlung (if the viscosity
decreases), or via SSC (if the viscosity increases). However, the latter
predicts a softer X-ray spectrum than was seen by Chandra, so it appears that a
bremsstrahlung origin for the X-ray outburst is favored. A strong correlation
is expected between the mm/sub-mm and X-ray fluxes when the flare X-rays are
produced by SSC, while the correlated variability is strongest between the
sub-mm/far-IR and X-rays when bremsstrahlung emission is dominant during the
flare. In addition, we shows that future coordinated multi-wavelength
observations planned for the 2002 and 2003 cycles may be able to distinguish
between the accretion and jet scenarios.
