Time Delay of QSO 0957+561 and Cosmological Implications

Abstract

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 di erent 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 BA = 424 3 days (1). We have used this time delay as well as a recent measurement of the 1D velocity dispersion of the main lensing galaxy (gal) to estimate H 0. Two H 0 = H 0 (BA ; gal) relations based on di erent pictures of the lens galaxy, lead to H 0 = 64 +14 ?15 km s ?1 Mpc ?1 (2) (softened power{law sphere) and H 0 = 66 +15 ?14 km s ?1 Mpc ?1 (2) (King pro le plus a point{mass at the center).

Gravitational Lenses and the Hubble Constant: Present and Future

“…The A component w as active (Kundic et al 1995), and also, we have not found evidences of strong microlensing in the r R comparison (Oscoz et al 1997, Goicoechea et al 1998. A similar result (417 3 days; 2 con dence level) has been derived by Kundic et al (1997).…”

“…Falco et al (1997) derived v (light) = 279 13 km/s, and so, with the whole lens model and the time delay above mentioned, one obtains H 0 = 66 +15 14 km/s/Mpc (2 ). This estimate is 10% accurate at 1 (Oscoz et al 1997). We h o w ever remark that a new lens model satisfying the constraints from radio mapping as well as new optical constraints deduced from HST observations is now in progress (Bernstein et al 1997).…”

“…Very recently, using image A data in the band r (1994( Dec.-1995 May, which w ere kindly provided us by T. Kundic), and our image B data in the band R (1996 Feb.-July), we concluded that BA = 424 3 d a ys (Oscoz et al 1997). The A component w as active (Kundic et al 1995), and also, we have not found evidences of strong microlensing in the r R comparison (Oscoz et al 1997, Goicoechea et al 1998.…”

“…The rough estimation BA T = 420 days (Pelt et al 1996; see also the paper by Pijpers in this volume) can be used for making nice datasets.…”

How accurate are the time delay estimates in gravitational lensing?

“…The Cross correlation method (Kundic et al 1997;Oscoz et al 1997), PRH method ) and Dispersion spectra (Pelt et al 1996), described in Sects. 3.1-3.3, respectively, have been widely used in the literature.…”