2005A&A...431..103J

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 Δτ=16±2days (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 (Ω_m, Ω_Λ)=(0.3, 0.7) cosmology, the time delay yields a Hubble parameter of H₀=60⁺⁹_–7(random, 1σ)±2(systematic)km/s/Mpc for a singular isothermal ellipsoid model and H₀=63⁺⁹_–7(random, 1σ)±1(systematic)km/s/Mpc 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, 1σ)±14(systematic)km/s/Mpc.