MILLIMETER FLARES AND VLBI VISIBILITIES FROM RELATIVISTIC SIMULATIONS OF MAGNETIZED ACCRETION ONTO THE GALACTIC CENTER BLACK HOLE

Abstract

The recent very long baseline interferometry (VLBI) observation of the Galactic center black hole candidate Sgr A* at 1.3 mm 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°). VLBI measurements on 2000–3000 km baselines should constrain the inclination. The data constrain the accretion rate to be (1.0–2.3) × 10 −9 M ☉ yr −1 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 0.5 hr rise times, 2–3.5 hr durations, and 40%–50% flux modulation, in agreement with observations of Sgr A* at millimeter wavelengths.