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

Creators: Burud, I.; Hjorth, J.; Courbin, F.; Cohen, J. G.; Magain, P.; Jaunsen, A. O.; Kaas, A. A.; Faure, C.; Letawe, G.

Abstract

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 (1σ) 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 Ω = 0.3, Λ = 0.7 cosmology, our time-delay measurement yields a Hubble constant of H_0 = 51 ± 9 km s^(-1) Mpc^(-1) (1σ error).

Additional Information

© 2002 ESO. Received: 23 April 2002. Accepted: 4 June 2002. We thank the NOT Director Vilppu Piirola for granting us observing time for this project on a flexible basis. We are especially grateful to the many visiting observers at NOT who have contributed to this project by performing the scheduled observations. This project was conceived in 1997 while JH and AOJ were visiting scientists at the Center for Advanced Study in Oslo. We thank Rolf Stabell and Sjur Refsdal for inviting us in their center and for their kind hospitality. JH appreciates the hospitality of the OMP where some of this work was conducted. The project was supported by the Danish Natural Science Research Council (SNF). IB was supported in part by contract ARC94/99-178 "Action de Recherche Concertée de la Communauté Française (Belgium)'' and Pôle d'Attraction Interuniversitaire, P4/05 (SSTC, Belgium). FC acknowledges financial support through Chilean grant FONDECYT/3990024 and through Marie Curie grant MCFI-2001-0242. Additional support from the European Southern Observatory and ECOS/CONICYT CU00U05 grant is also gratefully acknowledged.

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