An RXTE survey of long-term X-ray variability in Seyfert 1 galaxies

Data from the first three years of RXTE observations have been systematical ly analyzed to yield a set of 300 day 2-10 keV light curves with similarly uniform, similar to5 day sampling, for a total of nine Seyfert 1 galaxies. This is the first X-ray variability survey to probe consistently timescales longer than a few days in a large number of active galactic nuclei (AGNs). Comparison to ASCA data covering a similar band but much shorter (less tha n or similar to 1day) timescales shows that all the AGNs are more strongly variable on long timescales than on short timescales. This increase is grea test for the highest luminosity sources. The well-known anticorrelation bet ween source luminosity and variability amplitude is both stronger and shall ower in power-law slope when measured on long timescales. This is consisten t with a picture in which the X-ray variability of Seyfert 1 galaxies can b e can be described by a single, universal fluctuation power-density shape f or which the cutoff moves to longer timescales for higher luminosity source s. All of the Seyfert 1 galaxies exhibit stronger variability in the relati vely soft 2-4 keV band than in the harder 7-10 keV band. This effect is muc h too pronounced to be explained by simple models based either on the dilut ion of the power-law continuum by the Compton reflection component or on th e hard X-rays being produced in a static, pair-dominated, plane-parallel Co mptonizing corona.