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S. Nayakshin (NASA/GSFC), Mitchell C. Begelman (JILA, University of Colorado), D. Kazanas (NASA/GSFC)
We discuss the influence of the thermal ionization instability (see Nayakshin, Kazanas & Kallman 2000) on the studies of Fe K\alpha reverberation in AGN. We show that the density structure of the illuminated gas reacts {\em slowly} to changes in the incident X-rays, which leads to a very complex line variability behavior under certain conditions. We find that if X-ray luminosity of the source exceeds ~ a percent of the Eddington limit, then rapid variations in the X-ray flux will result in rather complex and observationally seemingly chaotic changes in the integrated flux of the line and its profile.
We also discuss the implications of our results for current and future Fe K\alpha line reverberations missions, such as Constellation-X. In particular, we point out the importance of the high energy part of the spectrum that is not going to be measured by Constellation-X. We show that AGN that are only moderately bright and/or have steep X-ray spectrum should be the best candidates in which to observe the line reverberation.
This work was supported by the National Research Council.
The author(s) of this abstract have provided an email address for comments about the abstract: serg@milkyway.gsfc.nasa.gov