Spectral variation of the seyfert 1 galaxy MCG -6-30-15 observed with suzaku

Abstract

We have investigated the spectral variation of the Seyfert 1 galaxy MCG -6-30-15 observed with Suzaku in 2006 January 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 a 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 was to make intensity-sliced spectra, and to study any correlation between the intensity and the spectral shape. The second approach was 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 6-10keV band and the spectral ratio of 0.5-3.0keV/6.0-10keV. Such a spectral variation requires a change of the apparent slope of the direct component, whereas the shape and intensity of the reflection component are invariable. The observed apparent spectral change is explained by the variation of the ionization degree of one of the two warm absorbers due to the intrinsic source luminosity variation. The current results suggest that the warm absorber has a critical role to explain the observed continuum spectral shape and the variation of MCG -6-30-15, which is essential to constrain the parameters of the putatively broadened iron line emission feature. © 2009. Astronomical Society of Japan.