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A. Markowitz, R. Edelson (University of California, Los Angeles), S. Vaughan (University of Leicester), K. Nandra (NASA Goddard Space Flight Center, Laboratory for High Energy Astrophysics)
RXTE has monitored the bright Seyfert~1 galaxy NGC~3516 once every 4.3 days since March 1997, with complementary even sampling on short and medium time scales earlier in the campaign. The first 1.5 yr of data were used to define the fluctuation power density spectrum (PDS) over time scales of hours to months (Edelson and Nandra 1999). This showed a knee corresponding to a characteristic variability time scale of ~1 month, but the location and shape of the turnover is poorly defined. In order to rectify this, we have used the full 3.5 yr of monitoring to extend the PDS to longer time scales by more than a factor of 2. We will discuss the implications for physical models of AGN variability, the relation of AGN variability to that seen to other accretion-powered objects like XRBs, and future prospects for measurement of the broad PDS in other AGN.