X-Ray Fluctuation Power Spectral Densities of Seyfert 1 Galaxies

By combining complementary monitoring observations spanning long, medium, and short timescales, we have constructed power spectraldensities (PSDs) of six Seyfert 1 galaxies. These PSDs span >~4orders of magnitude in temporal frequency, sampling variations ontimescales ranging from tens of minutes to over a year. In at least fourcases, the PSD shows a ``break,'' a significant departure from a powerlaw, typically on timescales of the order of a few days. This is similarto the behavior of Galactic X-ray binaries (XRBs), lower mass compactsystems with breaks on timescales of seconds. NGC 3783 shows tentativeevidence for a doubly broken power law, a feature that until now hasbeen seen only in the (much better defined) PSDs of low-state XRBs. Itis also interesting that (when one previously observed object is addedto make a small sample of seven) an apparently significant correlationis seen between the break timescale T and the putative black hole massMBH, while none is seen between break timescale andluminosity. The data are consistent with the linear relationT=MBH/106.5Msolar extrapolation over6-7 orders of magnitude is in reasonable agreement with XRBs. All ofthis strengthens the case for a physical similarity between Seyfert 1galaxies and XRBs.