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Data from the first three years of RXTE observations have been systematicallyanalyzed to yield a set of 300 day, 2-10 keV light curves with similarlyuniform, ~5 day sampling, for a total of nine Seyfert 1 galaxies. This is thefirst X-ray variability survey to consistently probe time scales longer than afew days in a large number of AGN. Comparison with ASCA data covering a similarband but much shorter (~1 day) time scales shows that all the AGN are morestrongly variable on long time scales than on short time scales. This increaseis greatest for the highest-luminosity sources. The well-known anticorrelationbetween source luminosity and variability amplitude is both stronger andshallower in power-law slope when measured on long time scales. This isconsistent with a picture in which the X-ray variability of Seyfert 1s can becan be described by a single, universal fluctuation power density shape forwhich the cutoff moves to longer time scales for higher luminosity sources. Allof the Seyfert 1s exhibit stronger variability in the relatively soft 2-4 keVband than in the harder 7-10 keV band. This effect is much too pronounced to beexplained by simple models based on either the dilution of the power-lawcontinuum by the Compton reflection component or on the hard X-rays beingproduced in a static, pair-dominated, plane-parallel Comptonizing corona.Comment: 18 pages, 9 figures. Accepted for publication in the Astrophysical  Journa

AnRXTESurvey of Long‐Term X‐Ray Variability in Seyfert 1 Galaxies