The Linear Polarization of Sagittarius A*. I. VLA Spectropolarimetry at 4.8 and 8.4 GHz

Synchrotron radiation from active galactic nuclei (AGN) is often highlypolarized. We present a search for linear polarization with the Very LargeArray (VLA) at 4.8 GHz and 8.4 GHz from the nearest AGN, Sagittarius A*. As apart of this study we used spectro-polarimetric data that were sensitive to arotation measure (RM) as large as 3.5 x 10^6 rad m^-2 at 4.8 GHz and 1.5 x 10^7rad m^-2 at 8.4 GHz. The upper limit to the linear polarization of Sgr A* overa broad range of RM is 0.2% at both frequencies. We also present continuumobservations with the VLA at 4.8 GHz which give an upper limit of 0.1% for RMsless than 10^4 rad m^-2. We conclude that depolarization is unlikely to occurin the Galacter Center scattering medium. However, it is possible fordepolarization to occur in the accretion region of Sgr A* if the outer scale ofturbulence is small enough. We also consider the implications of a very lowintrinsic polarization for Sgr A*.Comment: 16 pages, 3 figures, accepted for publication in the Astrophysical Journal, August 20, 1999, Vol 521 #