HEAD Division Meeting 1999, April 1999
Session 23. AGN
Oral, Tuesday, April 13, 1999, 2:00pm-3:34pm, Colonial Room

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[23.06] A Comprehensive Spectral and Variability Study of Narrow-line Seyfert 1 Galaxies Observed by ASCA

K. M. Leighly (Columbia University)

I present the results of a comprehensive and uniform analysis of 25 ASCA observations of 23 Narrow-line Seyfert 1 galaxies (NLS1s). The results generally support the hypothesis that the accretion rate relative to Eddington rate is larger in NLS1s compared with Seyfert 1s with broad optical lines. Time series analysis indicates that the excess variance, a parameter inversely related to the variability time scale, is typically an order of magnitude higher in NLS1s than in broad-line Seyfert 1s with the same X-ray luminosity. The light curves of some of the more variable objects are demonstratably non-Gaussian, a result that implys that those light curves are comprised of a small number of flares. A soft excess component is found in 17 of 19 unabsorbed objects; in contrast, such a hot soft excess is rarely observed in broad-line Seyfert galaxies. The strength of the soft excess, or the size of the excess above the hard X-ray power law, is correlated with the excess variance, a result that is independent of luminosity. It is confirmed that the hard X-ray photon index is consistently steeper in NLS1s, a result that supports a higher accretion rate in the context of two-phase Comptonization models, if that implys a stronger soft photon emission. Soft X-ray line emission and evidence for ionized iron K\alpha lines in a few objects supports reprocessing in a ionized accretion disk. A warm absorber appears to be less likely to be observed in NLS1s, and when observed, the ionization state is lower. This may be a consequence of a higher accretion rate in dynamical warm absorber models if the radiation pressure on warm absorber gas is so high that it is blown out of the nucleus.

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