Spectral Variation of the Seyfert 1 Galaxy MCG-6-30-15 observed with Suzaku

TL;DR

This study analyzes spectral variability of Seyfert 1 galaxy MCG-6-30-15 using Suzaku data, revealing that warm absorber ionization changes drive observed spectral variations, impacting models of its broad iron line emission.

Contribution

It demonstrates that ionization changes in warm absorbers explain spectral variability, highlighting their critical role in Seyfert galaxy X-ray spectra.

Findings

Spectral variation correlates with 6-10 keV intensity.

Reflection component remains stable while the direct component varies.

Ionization degree of warm absorbers changes with luminosity.

Abstract

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.