Title: COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses: XIV. Time delay of the doubly lensed quasar SDSS J1001+5027
Authors: Rathna Kumar, S. ×
Tewes, M.
Stalin, C. S.
Courbin, F.
Asfandiyarov, I.
Meylan, G.
Eulaers, E.
Prabhu, T.P.
Magain, P.
Van Winckel, Hans
Ehgamberdiev, Sh. #
Issue Date: Sep-2013
Publisher: EDP Sciences
Series Title: Astronomy & Astrophysics vol:557 pages:7
Article number: A44
Abstract: This paper presents optical R-band light curves and the time delay of the doubly imaged gravitationally lensed quasar SDSS J1001+5027 at a redshift of 1.838. We have observed this target for more than six years, between March 2005 and July 2011, using the 1.2-m Mercator Telescope, the 1.5-m telescope of the Maidanak Observatory, and the 2-m Himalayan Chandra Telescope. Our resulting light curves are composed of 443 independent epochs, and show strong intrinsic quasar variability, with an amplitude of the order of 0.2 magnitudes. From this data, we measure the time delay using five different methods, all relying on distinct approaches. One of these techniques is a new development presented in this paper. All our time-delay measurements are perfectly compatible. By combining them, we conclude that image A is leading B by 119.3 ± 3.3 days (1σ, 2.8% uncertainty), including systematic errors. It has been shown recently that such accurate time-delay measurements offer a highly complementary probe of dark energy and spatial curvature, as they independently constrain the Hubble constant. The next mandatory step towards using SDSS J1001+5027 in this context will be the measurement of the velocity dispersion of the lensing galaxy, in combination with deep Hubble Space Telescope imaging.

Based on observations made with the 2.0-m Himalayan Chandra Telescope (Hanle, India), the 1.5-m AZT-22 telescope (Maidanak Observatory, Uzbekistan), and the 1.2-m Mercator Telescope. Mercator is operated on the island of La Palma by the Flemish Community, at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.Light curves are only available at the CDS via anonymous ftp to ( or via
ISSN: 1432-0746
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Institute of Astronomy
× corresponding author
# (joint) last author

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