SAGITTARIUS A* ACCRETION FLOW AND BLACK HOLE PARAMETERS FROM GENERAL RELATIVISTIC DYNAMICAL AND POLARIZED RADIATIVE MODELING

摘要

We obtain estimates of Sgr A* accretion flow and black hole parameters by fitting polarized submillimeter observations with spectra computed using three-dimensional general relativistic (GR) magnetohydrodynamical (MHD) (GRMHD) simulations. Observations are compiled from averages over many epochs from reports in 29 papers for estimating the mean fluxes F ν, linear polarization (LP) fractions, circular polarization (CP) fractions, and electric vector position angles. GRMHD simulations are computed with dimensionless spins a * = 0, 0.5, 0.7, 0.9, 0.98 over a 20, 000M time interval. We perform fully self-consistent GR polarized radiative transfer using our new code to explore the effects of spin a *, inclination angle θ, position angle (P.A.), accretion rate , and electron temperature Te (Te is reported for radius 6M). By fitting the mean submillimeter fluxes and LP/CP fractions, we obtain estimates for these model parameters and determine the physical effects that could produce polarization signatures. Our best-bet model has a * = 0.5, θ = 75°, P.A. = 115°, , and Te = 3.1 × 1010 K at 6M. The submillimeter CP is mainly produced by Faraday conversion as modified by Faraday rotation, and the emission region size at 230?GHz is consistent with the very long baseline interferometry size of 37 μas. Across all spins, model parameters are in the ranges θ = 42°-75°, , and Te = (3-4) × 1010 K. Polarization is found both to help differentiate models and to introduce new observational constraints on the effects of the magnetic field that might not be fit by accretion models so far considered.