Variable Linear Polarization from Sagittarius A*: Evidence of a Hot Turbulent Accretion Flow

Abstract

We report the discovery of variability in the linear polarization from the Galactic center black hole source Sagittarius A*. New polarimetry obtained with the Berkeley-Illinois-Maryland Association array at a wavelength of 1.3 mm shows a position angle that differs by from observations 6 months prior and then remains 28 5 stable for 15 months. This difference may be due to a change in the source emission region on a scale of 10 Schwarzschild radii or due to a change of in the rotation measure. We consider a change in 5 2 3 # 10 rad m the source physics unlikely, however, since we see no corresponding change in the total intensity or polarized intensity fraction. On the other hand, turbulence in the accretion region at a radius ∼10R S-could readily 1000R S account for the magnitude and timescale of the position angle change.