K-band polarimetry of an Sgr A* flare with a clear sub-flare structure
Abstract
Context: .The supermassive black hole at the Galactic center, Sgr A*, shows frequent radiation outbursts, often called "flares". In the near-infrared some of these flares were reported as showing intrinsic quasi-periodicities. The flux peaks associated with the quasi-periodic behavior were found to be highly polarized.
Aims: .The aim of this work is to present new evidence to support previous findings of the properties of the polarized radiation from Sgr A* and to again provide strong support for the quasi-periodicity of 18± 3 min reported earlier.
Methods: .Observations were carried out at the European Southern Observatory's Very Large Telescope on Paranal, Chile. We used the NAOS/CONICA adaptive optics/near-infrared camera instrument. By fitting the polarimetric lightcurves with a hot-spot model, we addressed the question of whether the data are consistent with this model. To fit the observed data we used a general relativistic ray-tracing code in combination with a simple hot-spot/ring model.
Results: .We report on new polarization measurements of a K-band flare from the supermassive black hole at the Galactic center. The data provide very strong support for a quasi-periodicity of 15.5±2 min. The mean polarization of the flare is consistent with the direction of the electric field vector that was reported in previous observations. The data can be modeled successfully with a combined blob/ring model. The inclination i of the blob orbit must be i > 20° on a 3σ level, and the dimensionless spin parameter of the black hole is derived to be a_star > 0.5.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- November 2006
- DOI:
- 10.1051/0004-6361:20066251
- arXiv:
- arXiv:astro-ph/0610147
- Bibcode:
- 2006A&A...458L..25M
- Keywords:
-
- black hole physics;
- accretion;
- accretion disks;
- Galaxy: center;
- Astrophysics
- E-Print:
- accepted by A&