THE INFLUENCE OF MICROLENSING ON TIME-DELAY DETERMINATIONS IN DOUBLE-IMAGED QUASARS

The lag associated with the main peak of the cross-correlation functio n of the two light curves arriving from a double-imaged quasar is usua lly identified with the time delay between the components. However, sh ort-timescale microlensing events can independently modify the light c urve of each component, and when strong microlensing is present, the f eatures of the cross-correlation function depend on both amplitude and shape of the microlensing events. This fact prevents a direct interpr etation of the lag associated with the main peak as the true time dela y. We present a new analysis of the light curves cross-correlation fun ction including short-timescale microlensing, We discuss its applicati on to the 1995/1996 optical photometry of Q0957 + 561, and determine t he trend of a possible microlensing event taking place from JD 2,450,1 50 to 2,450,200.