Constraining the Accretion Flow in Sgr A* by General Relativistic Dynamical and Polarized Radiative Modeling

Details Constraining the Accretion Flow in Sgr A* by General Relativistic Dynamical and Polarized Radiative Modeling Constraining the Accretion Flow in Sgr A* by General Relativistic Dynamical and Polarized Radiative Modeling

2010-07-27

arxiv.org/abs/1007.4832v3

Astronomy and Astrophysics

Astrophysics

High Energy Astrophysical Phenomena

19 pages, 14 figures, substantially reworked, resubmitted to ApJ

Scientific paper

Constraints on the Sgr A* black hole and accretion flow parameters are found by fitting polarized sub-mm observations to three-dimensional (3D) general relativistic (GR) magnetohydrodynamical (MHD) (GRMHD) simulations. We compile a mean Sgr A* spectrum by averaging observations over many epochs from reports in 29 papers in order to determine the mean flux F_\nu, linear polarization (LP) fractions, circular polarization (CP) fractions, and electric vector position angles (EVPA). GRMHD simulations are run with dimensionless spins a*=0,0.5,0.7,0.9,0.98 over a 20000M time interval. We perform GR polarized radiative transfer using our new code to explore the spin a*, inclination angle theta, position angle (PA), accretion rate Mdot, and electron temperature T_e at radius 6M. We perform \chi^2 per degrees of freedom (dof) statistical analysis for 88GHz to 857GHz. Fitting mean fluxes (without LP and CP fractions) across all spins gives a best \chi^2/dof<1 and wide confidence intervals, which suggests that polarization may be crucial for constraining spin. Fitting with mean fluxes and LP and CP fractions favors spin a*=0.5 with 1) minimum \chi^2/dof=2.09 and 90% confidence intervals of \theta=60deg-69deg, PA=69deg-109deg, Mdot=(3.8-5.0)*10^{-8}Msun/yr, T_e=(3.4-4.2)*10^{10}K at 6M ; 2) CP being produced mainly by Faraday conversion ; and 3) an emission region size at 230GHz that is consistent with VLBI size of 37microas.

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