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Paper: X-ray Variability of Radio-quiet AGN
Volume: 373, The Central Engine of Active Galactic Nuclei
Page: 149
Authors: Uttley, P.
Abstract: The X-ray variability of radio-quiet AGN probes the region closest to the supermassive black hole. The variability is a noise process and no significant periodicities have been detected to date. Characteristic timescales are observed in the form of bends in the power-spectral densities (PSDs) of the excellent X-ray light curves provided over the last decade by the Rossi X-ray Timing Explorer and XMM-Newton. Here I review these advances in our understanding of AGN PSDs, by first demonstrating what PSDs mean in term of light curve behavior, and then describing the shape of AGN PSDs. I discuss the strong correlations between PSD bend-timescales, black hole mass and AGN luminosity. Remarkably, these correlations extrapolate to the timescales observed for black holes in X-ray binary systems (BHXRBs), proving the long-suspected link between stellar and supermassive black holes. Finally I discuss the PSD evidence that links radio-quiet AGN to the high/soft state of BHXRBs, and discuss whether the behavior of AGN is more similar to Cyg X-1 than transient BHXRBs.
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