Time Delay of QSO 0957+561 and Cosmological Implications

We obtain the time delay between the arrival time of the A and B images of the QSO 0957+561. The results of applying two different methods (the discrete cross-correlation function and the dispersion estimation technique) to the observed light curves of the A and B images are presented. The adopted value (time delay) is of ΔτBA = 424 ± 3 days (1 σ). We have used this time delay as well as a recent measurement of the one-dimensional velocity dispersion of the main lensing galaxy (σgal) to estimate H0. Two H0 = H0(ΔτBA, σgal) relations based on different pictures of the lens galaxy, lead to H0 = 64+ 14−15 km s-1 Mpc-1 (2 σ) (softened power-law sphere) and H0 = 66+ 15−14 km s-1 Mpc-1 (2 σ) (King profile plus a point-mass at the center).