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

We report the discovery of variability in the linear polarization from theGalactic Center black hole source, Sagittarius A*. New polarimetry obtainedwith the Berkeley-Illinois-Maryland Association array at a wavelength of 1.3 mmshows a position angle that differs by 28 +/- 5 degrees from observations 6months prior and then remains stable for 15 months. This difference may be dueto a change in the source emission region on a scale of 10 Schwarzschild radiior due to a change of 3 x 10^5 rad m^-2 in the rotation measure. We consider achange in the source physics unlikely, however, since we see no correspondingchange in the total intensity or polarized intensity fraction. On the otherhand, turbulence in the accretion region at a radius ~ 10 to 1000 R_s couldreadily account for the magnitude and time scale of the position angle change.Comment: accepted for publication in ApJ