Upper panel: ICCF (solid line) with its 1σ error (grey area) and ZDCF (black points) for the continuum and the Si IV emission line. Lower panel: same as in the upper panel, but for the continuum and the C IV emission line. The ZDCF is computed over 15 uncorrelated points per bin, and finds a simultaneous peak for the two emission features at days in the observer frame that is indicated in the plot (dashed line and dotted lines).