Adaptive PSF fitting – a highly performing photometric method and light curves of the GLS H1413+117: time delays and micro-lensing effects
Аннотация
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 <it>V</it>- and <it>R</it>-band light curves and <it>V</it>–<it>R</it> 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 <it>R</it>-band light curves over the seasons between 2003 and 2006. We have derived the new values: Δ<it>t</it><inf>AB</inf> = −17.4 ± 2.1, Δ<it>t</it><inf>AC</inf> = −18.9 ± 2.8 and Δ<it>t</it><inf>AD</inf> = 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 <f>$z_{\\rm l} = 1.95^{+0.06}_{-0.10}$</f> 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.