AAS 203rd Meeting, January 2004
Session 63 AGN
Oral, Tuesday, January 6, 2004, 10:00-11:30am, Regency VII

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[63.03] Long-Term X-ray Spectral Variability in Seyfert 1 Galaxies

A. Markowitz (UCLA/NASA-GSFC)

Direct time-resolved spectral fitting has been performed on continuous RXTE monitoring of seven Seyfert~1 galaxies in order to study their broadband spectral variability and Fe K\alpha variability characteristics on time scales of days to years. Variability in the Fe K\alpha line is not detected in some objects but is present in others, e.g., in NGC~3516, NGC~4151 and NGC~5548 there are systematic decreases in line flux by factors of ~2--5 over 3--4 years. The Fe K\alpha line varies less strongly than the broadband continuum, but, like the continuum, exhibits stronger variability towards longer time scales. Relatively less model-dependent broadband fractional variability amplitude (Fvar) spectra also show weaker line variability compared to the continuum variability. Comparable systematic long-term decreases in the line and continuum are present in NGC~5548. Overall, however, there is no evidence for correlated variability between the line and continuum, severely challenging models in which the line tracks continuum variations modified only by a light-travel time delay. Local effects such as the formation of an ionized skin at the site of line emission may be relevant. The spectral fitting and Fvar spectra both support spectral softening as continuum flux increases.

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.