M. Tewes, F. Courbin, G. Meylan
Measuring time delays between the multiple images of gravitationally lensed quasars is now recognized as a competitive way to constrain the cosmological parameters, well complementary with other cosmological probes. This requires long and well sampled optical light curves of numerous lensed quasars, e.g., as obtained by the COSMOGRAIL collaboration. High-quality data from our monitoring campaign calls for novel numerical techniques to robustly measure the delays as well as the associated random and systematic uncertainties, even in presence of microlensing variations. We propose three different point estimators to measure time delays, that are explicitly designed to handle light curves with extrinsic variability. These methods share a common formalism, which enables them to process data from n-image lenses. As the estimators rely on significantly contrasting ideas, we expect them to be sensitive to different bias sources. For each method and data set, we empirically estimate both the precision and accuracy (bias) of the time delay measurement using simulated light curves with known time delays that closely mimic the observations. Eventually, we test the self-consistency of our approach, and we demonstrate that our bias estimation is serviceable. These new methods, including the empirical uncertainty estimator, will represent the standard benchmark for the analysis of the COSMOGRAIL light curves.
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http://arxiv.org/abs/1208.5598
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