The influence of microlensing on time delay determinations in double-imaged quasars

The lag associated with the main peak of the cross-correlation function of the two light curves arriving from a double-imaged quasar is usually identified with the time delay between the components. However, short-timescale microlensing events can independently modify the light curve of each component, and when strong microlensing is present, the features of the cross-correlation function depend on both amplitude and shape of the microlensing events. This fact prevents a direct interpretation of the lag associated with the main peak as the true time delay. We present a new analysis of the light curves cross-correlation function including short-timescale microlensing, We discuss its application to the 1995/1996 optical photometry of Q0957 + 561, and determine the trend of a possible microlensing event taking place from JD 2,450,150 to 2,450,200.