Title: "Near-infrared polarimetry setting constraints on the model of an relativistically orbiting spot for Sgr A* flares"
The supermassive black hole at the Galactic center, Sgr A*, shows frequent
radiation outbursts, so-called flares. In the near-infrared some of these
flares were reported to show intrinsic quasi-periodicities of 18±3 min. In
2005 and 2006, we have carried out polarimetric observations of these QPOs
in the K-band. These observations allow for a detailed investigation of Sgr
A* within the hot spot model. In this model, inhomogeneities in the
accretion flow are represented as confined orbiting material. By
simultaneous fitting of the lightcurve fluctuations and the time-variable
polarization angle, we address the question whether these changes are
consistent with the hot spot model, in which the interplay of relativistic
effects plays the major role. We consider all general relativistic effects
that imprint on the polarization lightcurves. As the synchrotron mechanism
is most likely responsible for the intrinsic polarization, we consider two
different magnetic field configurations as approximations to the complex
structure of the magnetic field in the accretion flow onto Sgr A*.
Considering the quality of the fit, we think that the spot model is
favoured. Finally, our confidence contours give constraints to the
spin-parameter and the inclination of the supermassive black hole associated
with Sgr A*.