a) DCFs of each X-ray light curve (Swift/XRT (0.3–2 keV), Swift/XRT (2–10 keV) and RXTE/PCA (2–10 keV)), correlated with several optical and UV light curves, are averaged over all optical to UV bands and shown in black in the upper panel. The green lines represent the 1% and 99% extremes of the likewise averaged DCF distribution of simulated optical/UV light curves when correlated with the observed X-ray light curve. The blue lines represent the 5% and 95% extremes. Lower panel: z-transformed DCFs, which were, for the purpose of direct comparison with the DCF, rebinned to the same binning as the DCFs and averaged in the same way. b) Same as a), but all light curves have been detrended (as described in 4.3) before correlation.