[Previous] | [Session 4] | [Next]

[4.16] The Rapidly Variable X-ray Spectrum of MCG-6-30-15: Evidence for Variability in Both the Iron K-alpha Line Flux and Continuum Slope of MCG--6-30-15

R. Edelson (UCLA), S. Vaughan (Leicester Univ.)

Seyfert 1 galaxies often show strong gravitationally broadened iron fluorescence lines (e.g., Fabian et al. 2000). Because they are thought to arise near and be powered by the central continuum source, the lines would be expected to vary in response to the strong continuum variations (Reynolds 1999), but this is not generally observed. We investigated this further by developing a new method of spectral fitting on orbital time scales, and applied it to the currently best available data set, the 8 day quasi-continuous RXTE observation of MCG-6-30-15 (Lee et al. 2000). We find that the lines do indeed vary with smaller amplitude than the continuum, but the line and continuum variations do not appear correlated. This result has been extensively tested with detailed simulations, and appears to be quite robust. I will attempt to explain this surprising conclusion in the context of X-ray emission models and also field the inevitable questions about experimental technique. If there is time, I'll also discuss the spectral slope variability results, which suggest that the \Gamma-R correlation of Zdziarski et al. (1999) could be a spurious effect due to inadequate modeling of errors in the spectral fitting process.