Millimeter Flares and VLBI Visibilities from Relativistic Simulations of
  Magnetized Accretion onto the Galactic Center Black Hole
  The recent VLBI observation of the Galactic center black hole candidate Sgr
A* at 1.3mm shows source structure on event-horizon scales. This detection
enables a direct comparison of the emission region with models of the accretion
flow onto the black hole. We present the first results from time-dependent
radiative transfer of general relativistic MHD simulation data, and compare
simulated synchrotron images at black hole spin a=0.9 with the VLBI
measurements. After tuning the accretion rate to match the millimeter flux, we
find excellent agreement between predicted and observed visibilities, even when
viewed face-on (i < 30 degrees). VLBI measurements on 2000-3000km baselines
should constrain the inclination. The data constrain the accretion rate to be
(1.0-2.3)x10^-9 M_sun / yr with 99% confidence, consistent with but independent
of prior estimates derived from spectroscopic and polarimetric measurements.
Finally, we compute light curves, which show that magnetic turbulence can
directly produce flaring events with .5 hour rise times, 2-3.5 hour durations
and 40-50% flux modulation, in agreement with observations of Sgr A* at
millimeter wavelengths.
