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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2009
- DOI:
- 10.1088/0004-637X/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
- E-Print:
- 25 pages, 5 figures, ApJ accepted