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

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 28° ± 5° from observations 6 months prior and then remains 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 3 × 10 5 rad m -2 in the rotation measure. We consider a change in 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 ~10 R S -1000 R S could readily account for the magnitude and timescale of the position angle change.