Bower et al. 1999, The Linear Polarization of Sagittarius A* I.

The Linear Polarization of Sagittarius A* I. Spectro-polarimetric VLA Observations at 4.8 and 8.4 GHz

Bower G.C.(1,2), Backer D.C.(3), Zhao J.-H.(4), Goss M.(2), & Falcke H.(1)

(1) Max-Planck-Institut für Radioastronomie, Auf den Hüugel 69, D-53121 Bonn, Germany
(2) National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville, Socorro, NM 87801
(3) Astronomy Department \& Radio Astronomy Laboratory, University of California, Berkeley, CA 94720
(4) Harvard-Smithsonian Center for Astrophysics, Mail Stop 42, 60 Garden Street, Cambridge, MA 02138

Astrophysical Journal (1999), Vol. 521, p. 582


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*106 rad m-2 at 4.8 GHz and 1.5 107 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 104 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*.

Paper: Available in PostScript and (AAS)LaTex.

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