SIMBAD references

We have examined simultaneous X-ray and optical light curves of a sample of eight nearby Seyfert 1 galaxies observed using the European Photon Imaging Camera (EPIC) X-ray cameras and Optical Monitor onboard XMM-Newton. The observations span ∼1 d and revealed optical variability in four of the eight objects studied. In all the cases, the X-ray variability amplitude exceeded that of the optical both in fractional and in absolute luminosity terms. No clearly significant correlations were detected between wavebands using cross-correlation analysis. We conclude that, in three of the four objects in which optical variability was detected, reprocessing mechanisms between wavebands do not dominate either the optical or the X-ray variability on the time-scales probed.