  We have investigated spectral variation of the Seyfert 1 galaxy MCG-6-30-15
observed with Suzaku in January 2006 for three separate periods spreading over
fourteen days. We found that the time-averaged continuum energy spectrum
between 1 keV and 40 keV can be approximated with a spectral model composed of
the direct power-law component, its reflection component, two warm absorbers
with different ionization states, and neutral absorption. We have taken two
approaches to study its spectral variation at various timescales: The first
approach is to make intensity-sliced spectra and study correlation between the
intensity and spectral shape. The second approach is to study spectral changes
between the intervals when the source flux is above ("bright state") and below
("faint state") the average for fixed time-intervals. In both approaches, we
found a clear correlation between the intensity in the 6 -- 10 keV band and the
spectral ratio of 0.5 -- 3.0 keV/6.0-- 10 keV. Such a spectral variation
requires change of the apparent slope of the direct component, whereas the
shape and intensity of the reflection component being invariable. The observed
apparent spectral change is explained by variation of the ionization degree of
one of the two warm absorbers due to intrinsic source luminosity variation.
Current results suggest that the warm absorber has a critical role to explain
the observed continuum spectral shape and variation of MCG-6-30-15, which is
essential to constrain parameters of the putatively broadened iron line
emission feature.

High Energy Astrophysical Phenomena