EDP Sciences
Free access
Issue
A&A
Volume 391, Number 2, August IV 2002
Page(s) 481 - 486
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20020856


A&A 391, 481-486 (2002)
DOI: 10.1051/0004-6361:20020856

Time delay and lens redshift for the doubly imaged BAL quasar SBS 1520+530

I. Burud1, J. Hjorth2, F. Courbin3, 4, J. G. Cohen5, P. Magain3, A. O. Jaunsen6, A. A. Kaas7, C. Faure6, 8 and G. Letawe3

1  Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
2  Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
3  Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 août, Bat. B5C, Liège 1, Belgium
4  Universidad Católica de Chile, Departamento de Astronomia y Astrofisica, Casilla 306, Santiago 22, Chile
5  California Institute of Technology, Pasadena, CA 91125, USA
6  European Sourthern Observatory, Casilla 19, Santiago, Chile
7  Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Canary Islands, Spain
8  Observatoire Midi-Pyrénées, 14 avenue Édouard Belin, 31400 Toulouse, France

(Received 23 April 2002 / Accepted 4 June 2002 )

Abstract
We present optical R-band light curves of the gravitationally lensed quasar SBS 1520+530 derived from data obtained at the Nordic Optical Telescope. A time delay of $130\pm3$ days (1 $\sigma$) is determined from the light curves. In addition, spectra of SBS 1520+530 obtained at the Keck Observatory are spatially deconvolved in order to extract the spectrum of the faint lensing galaxy, free of any contamination by the light from the bright quasar images. This spectrum indicates a lens redshift z=0.717, in agreement with one of the absorption systems found in the quasar spectra. The best mass model of the system includes a second nearby galaxy and a cluster of galaxies in addition to the main lensing galaxy. Adopting this model and an $\Omega=0.3$, $\Lambda=0.7$ cosmology, our time-delay measurement yields a Hubble constant of $H_{0}=51 \pm 9~
{\rm km}~{\rm s^{-1}}~{\rm Mpc^{-1}}$ (1 $\sigma$ error).


Key words: gravitational lensing -- quasars: individual: SBS 1520+530 -- cosmology: cosmological parameters

Offprint request: I. Burud, burud@stsci.edu


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