Figure 1: A R-band image of SDSS J1650+4251 obtained at Maidanak Observatory. This image is a combination of 376 frames, totalising 31 h of exposure. The mean seeing is 1.0 , and the field of view is . The two stars labeled PSF1 and PSF2 are used to model the Point Spread Function required for the MCS deconvolution method. The 4 reference stars used for the photometric calibration are star #3, #4, PSF1 and PSF2. Star #5 is used as a cross-check of the deconvolution photometry. | |
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Figure 2: R-band light curves for the two quasar images in SDSS J1650+4251, as well as for a reference star in the field of view. The magnitudes are given in relative units. In order to avoid the points overlaps, the component B and the star curves have been shifted in magnitude. The 5 epochs marked by triangles deviate very far away from the otherwise smooth variations of the light curve of component B. They have been removed from the curves when determining the time delay (see Sect. 4). | |
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Figure 3: a) The dispersion function obtained when the normalisation of the light curves is determined directly from the data. Several local minima appear. A polynomial fit to the dispersion function (solid line) allows the determination of a time delay of days. b) The corresponding result of the Monte-Carlo simulation for 100 000 slightly modified light curves: 1.4 days. c) The dispersion function obtained for the light curves optimally shifted in magnitude (see text and Fig. 4). The function is now much smoother and has only one clear minimum at days. d) The corresponding Monte-Carlo simulation result and the final time delay estimate: 1.6 days. | |
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Figure 4: Value of the minimum of the dispersion function, as a function of the magnitude shift between the two light curves. A fit (solid line) to the measurements yields the optimal magnitude shift . In the figure, a shift of 0 corresponds to the normalisation carried out directly on the data. The dotted line and the vertical axis on the right give the corresponding value of the time delay days (for one single realisation of the Monte-Carlo simulation). | |
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Figure 5: a) Best polynomial fit to the light curves. The order of the Legendre polynomial is 5 for the first season and 4 for the second season. b) Result of the Monte-carlo simulation for 100 000 modified light curves, leading to a mean time delay of 2.2 days. c) Light curves shifted by the time delay and corrected for slow microlensing variations. d) Microlensing variations of quasar image B relative to quasar image A, taken as a slow linear trend over the whole period of observation. | |
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Figure 6: A zoom on the R-band image of SDSS J1650+4251 obtained at Maidanak Observatory (see Fig. 1). The positions of the quasar images are marked by white circles. The direction of the shear for our SIS+ and for the DV model is indicated by two lines. It does not point towards any specific galaxy in the field of view. Its large amplitude makes it mandatory to model the overall lensing potential. | |
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