RADIATIVE MODELS OF SGR A* FROM GRMHD SIMULATIONS

Abstract

Using flow models based on axisymmetric general relativistic magnetohydrodynamics simulations, we construct radiative models for Sgr A*. Spectral energy distributions (SEDs) that include the effects of thermal synchrotron emission and absorption, and Compton scattering, are calculated using a Monte Carlo technique. Images are calculated using a ray-tracing scheme. All models are scaled so that the 230 GHz flux density is 3.4 Jy. The key model parameters are the dimensionless black hole spin a * , the inclination i , and the ion-to-electron temperature ratio T i / T e . We find that (1) models with T i / T e = 1 are inconsistent with the observed submillimeter spectral slope; (2) the X-ray flux is a strongly increasing function of a * ; (3) the X-ray flux is a strongly increasing function of i ; (4) 230 GHz image size is a complicated function of i , a * , and T i / T e , but the T i / T e = 10 models are generally large and at most marginally consistent with the 230 GHz very long baseline interferometry (VLBI) data; (5) for models with T i / T e = 10 and i = 85° the event horizon is cloaked behind a synchrotron photosphere at 230 GHz and will not be seen by VLBI, but these models overproduce near-infrared and X-ray flux; (6) in all models whose SEDs are consistent with observations, the event horizon is uncloaked at 230 GHz; (7) the models that are most consistent with the observations have a * ∼ 0.9. We finish with a discussion of the limitations of our model and prospects for future improvements.