Abstract

Title: "Near-infrared polarimetry setting constraints on the model of an relativistically orbiting spot for Sgr A* flares"

Abstract:
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 183 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*.