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C. Matsumoto, H. Inoue (ISAS)
One of the most remarkable discoveries of ASCA is a broad and skewed feature around 5--7~keV in the spectrum of the Seyfert-1 galaxy MCG-6-30-15. This feature is well explained by considering that it is fluorescent lines coming from the innermost region of an accretion disk.
If this interpretation is correct, the study of this profile is very important. In order to confirm that the diskline interpretation is correct, we looked for firm evidence that the line feature is really a reprocessed emission from the continuum emission.
We analyzed the data sets of three long observations of the Seyfert-1 galaxy MCG-6-30-15 performed with ASCA. These observations had net exposure of 800~ks in total and provide us with the best data to investigate any correlations between the line properties and the continuum flux.
We investigated the variability of the line flux and the profile on a time scale of 2\times104~s. The line profile is approximated with a double-Gaussian model which consists of a relatively broad Red line and a relatively narrow Blue line. It was found that the Red line does not follow the continuum. Furthermore, the variability of the Red line is sometimes larger than that of the continuum. On the other hand, the Blue line flux is nearly proportional to the 7--10~keV flux and their correlation is significantly improved if we introduce a delay in the line flux to the continuum of about 104~s.
We also evaluated variability amplitude of the count rate on various time scales for 15~energy bands. We found the variability in 0.6--0.8~keV and 5--7~keV is relatively smaller than those in the other energy bands on a time scale of 105~s. To explain this reduced variability in the context of the diskline interpretation, an anti-correlation between the line flux and the continuum flux is required on the long time scale.
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