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 raytracing 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 iontoelectron 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 Xray flux is a strongly increasing function of a _{*}; (3) the Xray 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 nearinfrared and Xray 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.
 Publication:

The Astrophysical Journal
 Pub Date:
 November 2009
 DOI:
 10.1088/0004637X/706/1/497
 arXiv:
 arXiv:0909.5431
 Bibcode:
 2009ApJ...706..497M
 Keywords:

 accretion;
 accretion disks;
 black hole physics;
 Galaxy: center;
 MHD;
 radiative transfer;
 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 25 pages, 5 figures, ApJ accepted