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Paper: Non-linear variability and low-states in AGN: two sides of the same coin
Volume: 290, Active Galactic Nuclei: from Central Engine to Host Galaxy
Page: 131
Authors: Uttley, P.; McHardy, I.; Vaughan, S.
Abstract: Non-linearity in X-ray lightcurves of ultrasoft/NLS1 galaxies has been suspected for some time, but not proven. Recently, long-term X-ray monitoring observations of the NLS1 NGC4051 showed that besides showing possible evidence for non-linearity, the source also shows distinctive low-flux, low-variability `states' which last for months at a time. Here we show that both non-linearity and low states are a direct outcome of the remarkable linear relationship between RMS variability and flux which holds in lightcurves of AGN and X-ray binaries: AGN and XRB lightcurves are intrinsically non-linear, and can show low-states if the variability on all time-scales is large. We discuss physical interpretations of this result.
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