Universität zu Köln

Shahzamanian, B., Eckart, A., Valencia-S, M., Witzel, G., Zamaninasab, M., Sabha, N., Garcia-Marin, M., Karas, V., Karssen, G. D., Borkar, A., Dovciak, M., Kunneriath, D., Bursa, M., Buchholz, R., Moultaka, J. and Straubmeier, C. (2015). Polarized light from Sagittarius A(star) in the near-infrared K-s-band. Astron. Astrophys., 576. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

We present a statistical analysis of polarized near-infrared light from Sgr A*, the radio source associated with the supermassive black hole at the center of the Milky Way. The observations were carried out using the adaptive optics instrument NACO at the VLT UT4 in the infrared K-s-band from 2004 to 2012. Several polarized flux excursions were observed during these years. Linear polarization at 2.2 mu m, its statistics, and time variation, can be used constrain the physical conditions of the accretion process onto this supermassive black hole. With an exponent of about 4 for the number density histogram of fluxes above 5 mJy, the distribution of polarized flux density is closely linked to the single state power-law distribution of the total K-s-band flux densities reported earlier. We find typical polarization degrees on the order of 20% +/- 10% and a preferred polarization angle of 13 degrees +/- 15 degrees. Simulations show the uncertainties under a total flux density of similar to 2 mJy are probably dominated by observational effects. At higher flux densities there are intrinsic variations of polarization degree and angle within well constrained ranges. Since the emission is most likely due to optically thin synchrotron radiation, the preferred polarization angle we find is very likely coupled to the intrinsic orientation of the Sgr A* system, i.e. a disk or jet/wind scenario associated with the supermassive black hole. If they are indeed linked to structural features of the source the data imply a rather stable geometry and accretion process for the Sgr A* system.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Shahzamanian, B. UNSPECIFIED UNSPECIFIED UNSPECIFIED Eckart, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Valencia-S, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Witzel, G. UNSPECIFIED UNSPECIFIED UNSPECIFIED Zamaninasab, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Sabha, N. UNSPECIFIED UNSPECIFIED UNSPECIFIED Garcia-Marin, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Karas, V. UNSPECIFIED UNSPECIFIED UNSPECIFIED Karssen, G. D. UNSPECIFIED UNSPECIFIED UNSPECIFIED Borkar, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Dovciak, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kunneriath, D. UNSPECIFIED UNSPECIFIED UNSPECIFIED Bursa, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Buchholz, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Moultaka, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Straubmeier, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-408426
DOI:	10.1051/0004-6361/201425239
Journal or Publication Title:	Astron. Astrophys.
Volume:	576
Date:	2015
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language SGR-A-ASTERISK; SUPERMASSIVE BLACK-HOLE; STELLAR PROPER MOTIONS; X-RAY OBSERVATIONS; GALACTIC-CENTER; LINEAR-POLARIZATION; SYNCHROTRON-RADIATION; FLARING ACTIVITY; POSITION ANGLE; ORBITING SPOT Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/40842