An optical time delay for the double gravitational lens system FBQ 0951+2635*
Niels Bohr Institute, Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark e-mail: firstname.lastname@example.org
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
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 ± 2 days (1σ) 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 cosmology, the time delay yields a Hubble parameter of (random, ) (systematic) km s-1 Mpc-1 for a singular isothermal ellipsoid model and (random, ) (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 (random, ) (systematic) km s-1 Mpc-1.
Key words: gravitational lensing / galaxies: quasars: individual: FBQ 0951+2635 / cosmology: cosmological parameters
Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Based on observations made with ESO Telescopes at the Paranal Observatories under programme ID 66.A-0062(A). Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #7887.
© ESO, 2005