Estimating spin, disk inclination, and orientation using physical models of Sgr A*

Avery Broderick (Perimeter Institute) and Avi Loeb (Harvard) have modeled Sgr A* using Radiatively Inefficient Accretion Flows (RIAF) and then created images including full general relativistic ray-tracing. We've collaborated with them to fit RIAF models to the 1.3 mm VLBI data on Sgr A* to estimate parameters of the Sgr A* black hole and accretion disk. RIAF models are first constrained to fit the overall spectral energy density of Sgr A*, then fit to the 1.3 mm VLBI data. Model parameters include black hole spin, accretion disk inclination, and black hole spin axis orientation on the sky. First modeling efforts with the April 2007 data set placed limits on disk inclination, and when data from April 2009 are included, limits on black hole spin also become significant.

Broderick, Fish, Doeleman, Loeb, ApJ, v697, pp 45-54 (2009), "Estimating the Parameters of Sagittarius A*'s Accretion Flow Via Millimeter VLBI"

Broderick, Fish, Doeleman, Loeb, ApJ, v735, id 110 (2011), "Evidence for Low Black Hole Spin and Physically Motivated Accretion Models from Millimeter-VLBI Observations of Sagittarius A*"

Best fit models for Sgr A*: (Left) Chi-squared map of RIAF models fit to 2007 and 2009 1.3 mm VLBI data as a function of black hole spin and accretion disk inclination. The spin is less than 0.86 at 2σ significance, and the disk inclination is 68 degrees (+9, -28; 2σ). (Right) Image of the best fit RIAF model for Sgr A*.