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

Geoffrey C. Bower(1,2), Donald C. Backer(3), Jun-Hui Zhao(4), Miller Goss(2) & Heino Falcke(1)


(1) Max Planck Institut für Radioastronomie, Auf dem Hügel 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

Paper: to appear in ApJ 521 #2, Aug 20, 1999

Weblink: http://www.nrao.edu/~gbower/publications.html

EPrint Server: astro-ph/9904091

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\rdm at 4.8 GHz and 1.5* 107\rdm 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 \rdm. 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*.

Preprints available from the authors at gbower@aoc.nrao.edu , or the raw TeX (no figures) if you click here.

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