Confirmation and Analysis of Circular Polarization from Sagittarius A.pdf

Confirmation and Analysis of Circular Polarization from Sagittarius A* R.J. Sault 6 Australia Telescope National Facility, P.O. Box 76, Epping, NSW, 1710, Australia 0 0 2 and c e D J.-P. Macquart 8 2 Research Centre for Theoretical Astrophysics, School of Physics, University of Sydney, 2 NSW, 2006, Australia v 2 5 0 Received ; accepted 0 1 9 9 / h p - o r t s a : v i X r a – 2 – ABSTRACT Recently Bower et al. (1999b) have reported the detection of circular polarization from the Galactic Center black hole candidate, Sagittarius A*. We provide an independent confirmation of this detection, and provide some analysis on the possible mechanisms. Subject headings: Galaxy: center – polarization – radiation mechanisms: non-thermal – scattering – 3 – 1. Introduction The flat-spectrum, compact radio source in the Galactic Center, Sagittarius A* (Sgr A*), has long been believed to mark a massive black hole at the dynamical center of the Galaxy (Lynden-Bell Rees 1971). Eckart Genzel (1996,1997) and Ghez et al. (1998) provide compelling evidence that there is a dark mass of ≈ 2.6 × 106 M⊙ coincident with Sgr A*. Furthermore VLBI observations suggest the intrinsic size of Sgr A* is no larger than 1 to 3.6 AU (Krichbaum et al. 1998; Lo et al. 1998; Rogers et al. 1994; Bower Backer 1998). The observed size, however, is substantially larger as a result of scattering b