Adaptive PSF fitting - a highly performing photometric method and light curves of the GLS H1413+117: time delays and micro-lensing effects

Abstract

We present new photometric observations of H1413+117 acquired during seasons between 2001 and 2008 in order to estimate the time delays between the lensed quasar images and to characterize at best the on-going micro-lensing events. We propose a highly performing photometric method called the adaptive point spread function fitting and have successfully tested this method on a large number of simulated frames. This has enabled us to estimate the photometric error bars affecting our observational results. We analysed the V- and R-band light curves and V-R colour variations of the A-D components which show short- and long-term brightness variations correlated with colour variations. Using the χ² and dispersion methods, we estimated the time delays on the basis of the R-band light curves over the seasons between 2003 and 2006. We have derived the new values: Δt_AB = -17.4 ± 2.1, Δt_AC = -18.9 ± 2.8 and Δt_AD = 28.8 ± 0.7 d using the χ² method (B and C are leading, D is trailing) with 1σ confidence intervals. We also used available observational constraints (resp. the lensed image positions, the flux ratios in mid-IR and two sets of time delays derived in the present work) to update the lens redshift estimation. We obtained z_l = 1.95^{+0.06}_{-0.10} which is in good agreement with previous estimations. We propose to characterize two kinds of micro-lensing events: micro-lensing for the A, B, C components corresponds to typical variations of ∼10^-4 mag d^-1 during all the seasons, while the D component shows an unusually strong micro-lensing effect with variations of up to ∼10^-3 mag d^-1 during 2004 and 2005.