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 Delta tau(BA) = 424 +/- 3 days (1 sigma). We have used this time delay as well as a recent measurement of the one-dimensional velocity dispersion of the main lensing galaxy (sigma(gal)) to estimate H-0. Two H-0 = H-0(Delta tau(BA), sigma(gal)) relations based on different pictures of the lens galaxy, lead to H-0 = 64(-15)(+14) km s(-1) Mpc(-1) (2 sigma) (softened power-law sphere) and H-0 = 66(-14)(+15) km s(-1) Mpc(-1) (2 sigma) (King profile plus a point-mass at the center).