A Cutoo in the X-ray Fluctuation Power Density Spectrum of the Seyfert 1 Galaxy NGC 3516

Rick Edelson
RXTE observed the bright, strongly variable Seyfert 1 galaxy NGC 3516 once every 12.8 hr for 4.5 months and nearly continuously for a 4.2 day period in the middle, followed by ongoing monitoring once every 4.3 days. These data are used to construct the rst well-determined X-ray uctuation power density spectrum PDS of an active galaxy to span more than 4 decades of usable temporal frequency. The PDS shows a progressive attening of the power-law slope from 1.74 at short time scales to 0.73 at
more » ... er time scales, the clearest observation to date of the long-predicted cutoo in the PDS. The characteristic variability time scale is 1 month. The PDS appears similar to those seen for Galactic black hole candidates such as Cyg X-1, suggesting that these two classes of objects with very diierent luminosities and putative black hole masses diiering by more than a factor of 10 5 may have similar X-ray generation processes and structures. This RXTE experiment was only possible because of NGC 3516's special placement in the sky allowed quasi-continuous observations. Because of XMM's highly eccentric orbit, it will be possible to combine XMM and RXTE data will allow similar experiments for objects throughout the sky.