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Session 31 - Radiogalaxies - High Energy.
Oral session, Monday, January 13
We present analysis of the light curve from the ROSAT HRI monitoring observations of the broad-line radio galaxy 3C 390.3. Observed every three days for about 9 months, this is the first well sampled X-ray light curve on these time scales. The flares and quiescent periods in the light curve suggest that the variability is nonlinear, and a statistical test yields a detection with \sim 6 \sigma confidence. Evidence for X-ray reprocessing suggests that the X-ray emission is not from the compact radio jet, and the reduced variability before and after flares suggests there cannot be two components contributing to the X-ray short term variability. Thus, these results cannot be explained easily by simple models for AGN variability, including shot noise which may be associated with flares in disk-corona models or active regions on a rotating disk, because in those models the events are independent and the variability is therefore linear. The character of the variability is similar to that seen in Cygnus X-1, which has been explained by a reservoir or self-organized criticality model. Inherently nonlinear, this model can reproduce a 1/f^1.6-1.8 power spectrum and the reduced variability before and after the large flares. The 3C 390.3 light curve presented here is the first support for such models to explain AGN variability on intermediate time scales from a few days to months.
We also briefly discuss results from tests for nonlinear variability in light curves from other AGN, and the prospects for detecting nonlinear variability in AGN data from next generation all sky monitors.
Program listing for Monday