Title: COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses: XIII. Time delays and 9-yr optical monitoring of the lensed quasar RX J1131−1231
Authors: Tewes, M. ×
Courbin, F.
Meylan, G.
Kochanek, C.S.
Eulaers, E.
Cantale, N.
Mosquera, A.M.
Magain, P.
Van Winckel, Hans
Sluse, D.
Cataldi, G.
Vörös, D.
Dye, S. #
Issue Date: Aug-2013
Publisher: EDP Sciences
Series Title: Astronomy & Astrophysics vol:556 pages:10
Article number: A22
Abstract: We present the results from nine years of optically monitoring the gravitationally lensed zQSO = 0.658 quasar RX J1131-1231. The R-band light curves of the four individual images of the quasar were obtained using deconvolution photometry for a total of 707 epochs. Several sharp quasar variability features strongly constrain the time delays between the quasar images. Using three different numerical techniques, we measured these delays for all possible pairs of quasar images while always processing the four light curves simultaneously. For all three methods, the delays between the three close images A, B, and C are compatible with being 0, while we measured the delay of image D to be 91 days, with a fractional uncertainty of 1.5% (1σ), including systematic errors. Our analysis of random and systematic errors accounts in a realistic way for the observed quasar variability, fluctuating microlensing magnification over a broad range of temporal scales, noise properties, and seasonal gaps. Finally, we find that our time-delay measurement methods yield compatible results when applied to subsets of the data.

Based on observations made with the 1.2-m Swiss Euler telescope (La Silla, Chile), the 1.3-m SMARTS telescope (Las Campanas, Chile), 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 available at the CDS via anonymous ftp to ( or via
ISSN: 0004-6361
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Institute of Astronomy
× corresponding author
# (joint) last author

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