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 highly polarized. We present a search for linear polarization with the Very Large Array (VLA) at 4.8 GHz and 8.4 GHz from the nearest AGN, Sagittarius A*. As a part of this study we used spectro-polarimetric data that were sensitive to a rotation measure (RM) as large as 3.5 × 10 6 rad m −2 at 4.8 GHz and 1.5 × 10 7 rad m −2 at 8.4 GHz. The upper limit to the linear polarization of Sgr A * over a broad range of RM is 0.2 % at both frequencies. We also present continuum observations with the VLA at 4.8 GHz which give an upper limit of 0.1 % for RMs less than 10 4 rad m −2. We conclude that depolarization is unlikely to occur in the Galacter Center scattering medium. However, it is possible for depolarization to occur in the accretion region of Sgr A * if the outer scale of turbulence is small enough. We also consider the implications of a very low intrinsic polarization for Sgr A*. Subject headings: Galaxy: center — galaxies: active — scattering — polarization 1.