The polarization properties of sgr A* at submillimeter wavelengths

Abstract

We have placed an upper limit on the magnitude of the rotation measure of 7 × 105 rad m-2 for the putative Faraday screen (magnetized plasma) in front of Sgr A*, the radio source associated with the black hole in the Galactic Center. There is evidence that the actual rotation measure is about -5 × 105 rad m-2. With a simple model of equipartition of energy and reasonable inner radius for the screen, the accretion rate is estimated to be less than 10-6 M⊙ yr -1. In addition, we have detected, for the first time, intra-day variability in the polarization of Sgr A*, which may be due to either intrinsic variations in Sgr A* or variations in the composition of the Faraday screen. © 2008 Springer-Verlag Berlin Heidelberg.