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

Abstract:

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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Questions: Heino Falcke, hfalcke@mpifr-bonn.mpg.de