Normalised light curves in the r′ (top), He (middle) and u′ (bottom) filters versus orbital phase at a resolution of 9.7 s. The source light curve has been divided by the comparison one. Note that the vertical scale is logarithmic. The observations are spread over four different orbital cycles but split over two different nights (the vertical line indicates the gap of 27 orbital cycles). The different bright phase intervals (B1 to B5) are labelled.