Radiative models of SGR A* from grmhd simulations

Monika Mościbrodzka, Charles F. Gammie, Joshua C. Dolence, Hotaka Shiokawa, Po Kin Leung

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish (US)
Pages (from-to)497-507
Number of pages11
JournalAstrophysical Journal
Issue number1
StatePublished - 2009

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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