On X‐Ray Variability in Seyfert Galaxies

This paper presents a quantification of the X-ray variability amplitude for79 ASCA observations of 36 Seyfert 1 galaxies. We find that consideration ofsources with the narrowest permitted lines in the optical band introducesscatter into the established correlation between X-ray variability and nuclearluminosity. Consideration of the X-ray spectral index and variabilityproperties together shows distinct groupings in parameter space for broad andnarrow-line Seyfert 1 galaxies, confirming previous studies. A strongcorrelation is found between hard X-ray variability and FWHM Hbeta. A range ofnuclear mass and accretion rate across the Seyfert population can explain thedifferences observed in X-ray and optical properties. An attractive alternativemodel, which does not depend on any systematic difference in central mass, isthat the circumnuclear gas of NLSy1s is different to BLSy1s in temperature,optical depth, density or geometry.Comment: 11 pages, 1 figure 1 table. LaTeX with encapsulated postscript. Accepted for publication in the Astrophysical Journal. Replaced first version to fix a printing problem caused by the figure. Figure content is the same as befor