Mulit-wavelength light curves of NGC 5548. Top and bottom panels: the observed X-ray and UV light curves normalised to their mean (H1, H3, and UVW2 bands are plotted in red, orange, and blue points, respectively). The vertical dotted lines indicate the times at which we selected the UV data points. The grey shaded areas show the corresponding time intervals over which we integrated the X-ray spectrum (see text for details).