Volume 585, January 2016
|Number of page(s)
|Numerical methods and codes
|23 December 2015
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses
XV. Assessing the achievability and precision of time-delay measurements
1 Laboratoire d’astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
2 Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
3 Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, B5c, 4000 Liège, Belgium
Received: 9 June 2015
Accepted: 28 September 2015
COSMOGRAIL is a long-term photometric monitoring of gravitationally lensed quasars aimed at implementing Refsdal’s time-delay method to measure cosmological parameters, in particular H0. Given the long and well sampled light curves of strongly lensed quasars, time-delay measurements require numerical techniques whose quality must be assessed. To this end, and also in view of future monitoring programs or surveys such as the LSST, a blind signal processing competition named Time Delay Challenge 1 (TDC1) was held in 2014. The aim of the present paper, which is based on the simulated light curves from the TDC1, is double. First, we test the performance of the time-delay measurement techniques currently used in COSMOGRAIL. Second, we analyse the quantity and quality of the harvest of time delays obtained from the TDC1 simulations. To achieve these goals, we first discover time delays through a careful inspection of the light curves via a dedicated visual interface. Our measurement algorithms can then be applied to the data in an automated way. We show that our techniques have no significant biases, and yield adequate uncertainty estimates resulting in reduced χ2 values between 0.5 and 1.0. We provide estimates for the number and precision of time-delay measurements that can be expected from future time-delay monitoring campaigns as a function of the photometric signal-to-noise ratio and of the true time delay. We make our blind measurements on the TDC1 data publicly available.
Key words: methods: data analysis / gravitational lensing: strong / cosmological parameters
© ESO, 2015
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