Subtracted cross-correlation of the EPIC pn (X-ray) and OM (UV) light curves (see the text for details). The residuals of the fits to the cross-correlations are displayed for RU Peg, WW Cet, T Leo, and VW Hyi from the top to the bottom of the figure. Single Lorenzian fits applied are shown as solid black lines (SS Cyg has been excluded since only a single Lorentzian was already used). The reduced χ² values of the fits are given in Table 2.