Roman V. Shcherbakov, Robert F. Penna, Jonathan C. McKinney
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.
View original:
http://arxiv.org/abs/1007.4832
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