  Previous observations with the Rossi X-ray Timing Explorer (RXTE) have
suggested that the power spectral density (PSD) of NGC 3783 flattens to a slope
near zero at low frequencies, in a similar manner to that of Galactic black
hole X-ray binary systems (GBHs) in the `hard' state. The low radio flux
emitted by this object, however, is inconsistent with a hard state
interpretation. The accretion rate of NGC 3783 (~7% of the Eddington rate) is
similar to that of other AGN with `soft' state PSDs and higher than that at
which the GBH Cyg X-1, with which AGN are often compared, changes between
`hard' and `soft' states (~2% of the Eddington rate). If NGC 3783 really does
have a `hard' state PSD, it would be quite unusual and would indicate that AGN
and GBHs are not quite as similar as we currently believe. Here we present an
improved X-ray PSD of NGC 3783, spanning from ~10^{-8} to ~10^{-3} Hz, based on
considerably extended (5.5 years) RXTE observations combined with two orbits of
continuous observation by XMM-Newton. We show that this PSD is, in fact, well
fitted by a `soft' state model which has only one break, at high frequencies.
Although a `hard' state model can also fit the data, the improvement in fit by
adding a second break at low frequency is not significant. Thus NGC 3783 is not
unusual. These results leave Arakelian 564 as the only AGN which shows a second
break at low frequencies, although in that case the very high accretion rate
implies a `very high', rather than `hard' state PSD. The break frequency found
in NGC 3783 is consistent with the expectation based on comparisons with other
AGN and GBHs, given its black hole mass and accretion rate.
