Time Delays in the Gravitationally Lensed Quasar H1413+117 (Cloverleaf)
Abstract
The quadruple quasar H1413+117 (z_{s} = 2.56) has been monitored with the 2.0 m Liverpool Telescope in the r Sloan band from 2008 February to July. This optical followup leads to accurate light curves of the four quasar images (AD), which are defined by 33 epochs of observation and an average photometric error of ~15 mmag. We then use the observed (intrinsic) variations of ~50100 mmag to measure the three time delays for the lens system for the first time (1σ confidence intervals): Δτ_{ AB } = 17 ± 3, Δτ_{ AC } = 20 ± 4, and Δτ_{ AD } = 23 ± 4 days (Δτ_{ ij } = τ_{ j }  τ_{ i }; B and C are leading, while D is trailing). Although time delays for lens systems are often used to obtain the Hubble constant (H _{0}), the unavailability of the spectroscopic lens redshift (z_{l} ) in the system H1413+117 prevents a determination of H _{0} from the measured delays. In this paper, the new timedelay constraints and a concordance expansion rate (H _{0} = 70 km s^{1} Mpc^{1}) allow us to improve the lens model and to estimate the previously unknown z_{l} . Our 1σ estimate z_{l} = 1.88^{+0.09} _{0.11} is an example of how to infer the redshift of very distant galaxies via gravitational lensing.
 Publication:

The Astrophysical Journal
 Pub Date:
 January 2010
 DOI:
 10.1088/0004637X/708/2/995
 arXiv:
 arXiv:0911.4829
 Bibcode:
 2010ApJ...708..995G
 Keywords:

 gravitational lensing;
 quasars: individual: H1413+117;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 12 pages, 4 figures, 3 tables, accepted for publication in ApJ