EDP Sciences
Free access
Volume 431, Number 1, February III 2005
Page(s) 103 - 109
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20041432

A&A 431, 103-109 (2005)
DOI: 10.1051/0004-6361:20041432

An optical time delay for the double gravitational lens system FBQ 0951+2635

P. Jakobsson1, 2, J. Hjorth1, I. Burud3, G. Letawe4, C. Lidman5 and F. Courbin6

1  Niels Bohr Institute, Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
    e-mail: pallja@astro.ku.dk
2  Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavík, Iceland
3  Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
4  Institut d'Astrophysique et de Géophysique, ULg, Allée du 6 Août 17, B5C, 4000 Sart Tilman (Liège), Belgium
5  European Southern Observatory, Casilla 19, Santiago, Chile
6  Laboratoire d'Astrophysique, École Polytechnique Fédérale de Lausanne, Observatoire, 1290 Chavannes-des-bois, Switzerland

(Received 8 June 2004 / Accepted 13 October 2004)

We present optical R-band light curves of the double gravitationally lensed quasar FBQ 0951+2635 from observations obtained at the Nordic Optical Telescope between March 1999 and June 2001. A time delay of $\Delta \tau = 16$  $\pm$ 2 days (1 $\sigma$) is determined from the light curves. New constraints on the lensing geometry are provided by the position and ellipticity of the lensing galaxy. For a $(\Omega_{{\rm m}}, \Omega_{\Lambda})= (0.3, 0.7)$ cosmology, the time delay yields a Hubble parameter of H0 = 60+9-7  (random, $1 \sigma$$\pm
2$  (systematic) km s -1 Mpc -1 for a singular isothermal ellipsoid model and H0 = 63+9-7 (random, $1 \sigma$$\pm
1$  (systematic) km s -1 Mpc -1 for a constant mass-to-light ratio model. In both models, the errors are mainly due to the time-delay uncertainties. Non-parametric models yield H0 = 64+9-7  (random, $1 \sigma$$\pm 14$ (systematic) km s -1 Mpc -1.

Key words: gravitational lensing -- galaxies: quasars: individual: FBQ 0951+2635 -- cosmology: cosmological parameters

© ESO 2005

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