A novel approach for extracting time-delays from lightcurves of lensed quasar images

¹ Institut d'Astrophysique et de Géophysique, Université de Liège, Avenue de Cointe 5, 4000 Liège, Belgium e-mail: magain@astro.ulg.ac.be; sohy@astro.ulg.ac.be
² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA e-mail: burud@stsci.edu
³ Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark e-mail: jens@astro.ku.dk

Corresponding author: I. Burud, burud@astro.ulg.ac.be

Received: 21 May 2001
Accepted: 15 October 2001

Abstract

We present a new method to estimate time delays from light curves of lensed quasars. The method is based on minimization between the data and a numerical model light curve. A linear variation can be included in order to correct for slow long-term microlensing effects in one of the lensed images. An iterative version of the method can be applied in order to correct for higher-order microlensing effects. The method is tested on simulated light curves. When higher-order microlensing effects are present, the time delay is best constrained with the iterative method. Analysis of a published data set for the lensed double Q 0957+561 yields results in agreement with other published estimates.