Bottom panel: net U band light curve with a 10 s binning time. Count rates are normalized to the average persistent quiescence value. A sinusoidal fit with a period of 6.4 h is also reported. Gaps are due to the OM fast acquisition mode. Middle panel: the EPIC-pn net light curve in the 0.3 − 10 keV range with a 10 s binning time. The count rate is normalized to the average quiescent value. Flares are marked in cyan, dips with no spectral change in magenta, dips showing a softening are marked in blue, while hard dips are marked in red. Arrows mark ten long dips used to study the CCF and spectra. Top panel: the hardness ratio between the 0.3 − 2 keV and 2 − 10 keV bands with binning time of 60 s. (See electronic edition for colour version.)