On the orientation of the Sagittarius A* system

¹ I.Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany e-mail: leo@ph1.uni-koeln.de
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ Institut für Theoretische Physik und Astrophysik, Universität zu Kiel, 24098 Kiel, Germany
⁴ Steward Observatory, The University of Arizona, 933 N. Cherry Ave. Tucson, AZ 85721, USA
⁵ Astronomical Institute, Academy of Sciences, Boční II, 14131 Prague, Czech Republic

Received: 4 June 2007
Accepted: 15 August 2007

Abstract

Context.The near-infrared emission from the black hole at the Galactic center (Sgr A*) has unique properties. The most striking feature is a suggestive periodic sub-structure that has been observed in a couple of flares so far.

Aims.Using near-infrared polarimetric observations and modelling the quasi-periodicity in terms of an orbiting blob, we try to constrain the three dimensional orientation of the Sgr A* system.

Methods.We report on so far unpublished polarimetric data from 2003. They support the observations of a roughly constant mean polarization angle of ~ ± from 2004–2006. Prior investigations of the 2006 data are deepened. In particular, the blob model fits are evaluated such that constraints on the position angle of Sgr A* can be derived.

Results.Confidence contours in the position – inclination angle plane are derived. On a  level the position angle of the equatorial plane normal is in the range ~ (east of north) in combination with a large inclination angle. This agrees well with recent independent work in which radio spectral/morphological properties of Sgr A* and X-ray observations, respectively, have been used. However, the quality of the presently available data and the uncertainties in our model bring some ambiguity to our conclusions.