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P. Uttley, I. M. McHardy (University of Southampton)
X-ray timing studies of AGN are providing new insights into the deep similarities between AGN and galactic black hole candidates (GBHCs), which we discuss here. We have monitored a selection of Seyfert galaxies with RXTE since 1996, sampling on a range of time-scales to measure their broadband power spectra for the very first time. Results from the first four years of our campaign showed that the power spectra flatten towards low frequencies, like those of GBHCs, have the same RMS amplitude as GBHCs and that the characteristic power-spectral break frequency scales inversely with black hole mass, implying that the inner regions of AGN and GBHCs are essentially identical, with variability time-scales scaling linearly with black hole mass.
This year we continued our RXTE monitoring program with 2 months of intensive (6-hourly) monitoring on each of our targets. Combining these data with our long-term program, we confirm another parallel with GBHCs - the existence of different accretion states. In one of our targets (NGC~5506), we measure a power-spectrum analogous to those of GBHCs in the high state, while in NGC~4051 - which we have previously seen in two unusual low states lasting several months - we confirm significant changes in power-spectral shape during the course of our monitoring campaign, which suggest an analogy with the exotic galactic micro-quasars. The existence of a variety of accretion states in AGN, analogous to those seen in GBHCs, has important implications for AGN unification.
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