Time delay and lens redshift for the doubly imaged BAL quasar SBS 1520+530

Burud, I., Hjorth, J., Courbin, F., Cohen, J. G., Magain, P., Jaunsen, A. O., Kaas, A. A., Faure, C., and Letawe, G.
Astronomy and Astrophysics, v.391, p.481-486 (2002)


We present optical R-band light curves of the gravitationally lensed quasar SBS 1520+530 derived from data obtained at the Nordic Optical Telescope. A time delay of 130+/-3 days (1sigma ) is determined from the light curves. In addition, spectra of SBS 1520+530 obtained at the Keck Observatory are spatially deconvolved in order to extract the spectrum of the faint lensing galaxy, free of any contamination by the light from the bright quasar images. This spectrum indicates a lens redshift z=0.717, in agreement with one of the absorption systems found in the quasar spectra. The best mass model of the system includes a second nearby galaxy and a cluster of galaxies in addition to the main lensing galaxy. Adopting this model and an Omega =0.3, Lambda =0.7 cosmology, our time-delay measurement yields a Hubble constant of H0=51 +/- 9 km s-1 Mpc-1 (1sigma error). Based on observations made with the Nordic Optical, 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 and the W. M. Keck Observatory which is operated jointly by the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. Table 2 is only available in electronic form at the CDS via anonymous ftp to ( or via