  The first seven years of RXTE monitoring of Seyfert 1 active galactic nuclei
have been systematically analyzed to yield five homogeneous samples of 2-12 keV
light curves, probing hard X-ray variability on successively longer durations
from ~1 day to ~3.5 years. 2-10 keV variability on time scales of ~1 day, as
probed by ASCA, are included. All sources exhibit stronger X-ray variability
towards longer time scales, but the increase is greater for relatively higher
luminosity sources. Variability amplitudes are anti-correlated with X-ray
luminosity and black hole mass, but amplitudes saturate and become independent
of luminosity or black hole mass towards the longest time scales. The data are
consistent with the models of power spectral density (PSD) movement described
in Markowitz et al. (2003a) and McHardy et al. (2004), whereby Seyfert 1
galaxies' variability can be described by a single, universal PSD shape whose
break frequency scales with black hole mass. The best-fitting scaling relations
between variability time scale, black hole mass and X-ray luminosity imply an
average accretion rate of ~5% of the Eddington limit for the sample. Nearly all
sources exhibit stronger variability in the relatively soft 2-4 keV band
compared to the 7-12 keV band on all time scales. There are indications that
relatively less luminous or less massive sources exhibit a greater degree of
spectral variability for a given increase in overall flux.
