X-ray light curves for the 15 XMM-Newton observations (numbered on top), artificially joined in time, with dates in September and October 2009 indicated at the bottom. The cumulative exposure time since the start of the first observation is reported in abscissa. The upper (black) curve shows the pn count rate, while the lower (red) curve refers to the mos1 detector. All time bins have the same nominal duration of 600 s. The symbols on top indicate the strictly simultaneous optical spectroscopy (triangles for SARG, squares for du Pont, diamonds for ESPaDOnS observations).