Figure 1: Interpolation cross-correlation functions of B and R-band light curves as functions of the time delays (in days). A positive time delay indicates B-band leading the R-band. The scale is the same for all objects. | |
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Figure 8: Distribution of the time delays (ICCF peak positions) between B and R-bands. A positive time lag means the blue-band light curve leads the red one. A Gaussian fit to the distribution is shown (one deviating object omitted). The shaded area shows the distribution of the well-sampled (N>35) objects only (see the text). | |
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Figure 10: Various realizations of ICCF as functions of the time delay (in days) for PG 0804+761, obtained by adding appropriate random noise to the light curves (simulating the photometric errors) - the left panel and using a random sub sample of the original sample (simulating scarcely observed cases) - 50% ( the middle panel) and 25% ( the right panel). One sees that both effects, although influential, do not significantly alter the final result. For that particular case, the photometric error effect appears to be responsible for 0.4 days uncertainty in the ICCF peak position, while the reduction of the original sample by a half - for 1.3 days and by 75% - for 3.3 days. In order to check the compatibility, the discrete cross-correlation method was also applied to the PG 0804+761 light curves (open symbols with error bars; the left panel). Here the peak cannot be defined so clearly, but the general shape of the curve is very similar. The slight vertical offset between the ICCF and the DCCF is perhaps a binning artifact (the time over which the DCCF is averaged is 20 days) and does not seem to affect the peak position. | |
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Figure 14: Normalized difference between the observed and the expected time lags as functions of different quasar properties. The figure shows the influence of the number of the observations, N ( top-left panel, objects are separated by their black hole masses) and radio-loudness (Kellermann index, middle-left; Kellermann et al. 1989); (B-R) color ( bottom-left); H line width (in km s^{-1}, top-right); soft X-ray spectral index ( middle-right); red shift ( bottom-right) - all they shown with different symbols, separated by the number of the observations. As the top-left panel shows, the scatter between the observed and the expected times is significant only for N<35, so this value is further used in the remaining panels as a separation criterion between the well-sampled and the under-sampled objects. | |
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