Rapid X-ray variability in Seyfert galaxies

The rapid and seemingly random fluctuations in X-ray luminosity of Seyfert galaxies provided early support for the standard model in which Seyferts are powered by a supermassive black hole fed from an accretion disc. However, since EXOSAT there has been little opportunity to advance our understanding of the most rapid X-ray variability. Observations with XMM-Newton have changed this. Quantitative analysis shows the properties of Seyfert variability are similar to those of Galactic X-ray binaries, suggesting similar processes operate in the two types of sources. We will discuss some recent results obtained from XMM-Newton observations of Seyfert 1 galaxies. Particular attention will be given to the remarkable similarity found been the timing properties of Seyferts and black hole X-ray binaries, including the power spectrum and the cross spectrum (time delays and coherence), and their implications for the physical processes at work in Seyferts. Time pending, we will also discuss some of the remarkable non-linear properties of Seyfert variability.