Another interpretation of the disk-line profile for the Seyfert 1 galaxy MCG-6-30-15

The Seyfert 1 galaxy MCG-6-30-15 is a representative object possessing a "disk-line" (a broad and skewed feature around 5-7keV in an X-ray spectrum). Using the longest MCG-6-30-15 observation with ASCA, Matsumoto et al. (2003, PASJ, 55, 615) found an interesting time-variability: the RMS variability as a function of a time-bin-width decreases more rapidly in the disk-line energy band (5.0-6.6 keV) than those in the other energy bands, as the time-bin-width increases from similar to 10(4) s to similar to 10(5) s. In this paper, we argue that this energy-dependent change in the RMS variability as a function of the time-bin-width is difficult to be reproduced by simply considering the variability of a "disk-line", but that the RMS variability of the continuum component should have an energy-dependent evolution associated with the time-bin-width change. Such an energy-dependent variability of the continuum component can be realized by introducing absorption components with the typical variation time scale longer than that of the continuum. In this interpretation, a significant part of the broad excess feature in 5-7 keV is considered to be the result of a transparent spectral window of the warm absorbers.