Radiative Models of Sgr A* from GRMHD Simulations

Monika Moscibrodzka(1), Charles F. Gammie(1,2), Joshua C. Dolence(2), Hotaka Shiokawa(2), Po Kin Leung(2)

(1) Department of Physics, University of Illinois, 1110 West Green Street, Urbana, IL 61801
(2) Astronomy Department, University of Illinois, 1002 West Green Street, Urbana, IL 61801

Paper: ApJ, Oct 2009, in press

EPrint Server: 0909.5431


Using flow models based on axisymmetric general relativistic magnetohydrodynamics (GRMHD) simulations, we construct radiative models for Sgr A*. Spectral energy distributions 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 Trat. We find that: (1) models with Trat = 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 Trat, but the Trat = 10 models are generally large and at most marginally consistent with the 230 GHz VLBI data; (5) for models with Trat = 10 and i = 85 DEG the event horizon is cloaked behind a synchrotron photosphere at 230 GHz and will not be seen by VLBI, but these models overproduce NIR 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.

Preprints available from the authors at mmosc@illinois.edu , or the raw TeX (no figures) if you click here.

Back to the gcnews home-page.