Suzaku view of X-ray Spectral Variability of the Radio Galaxy Centaurus A : Partial Covering Absorber, Reflector, and Possible Jet Component

TL;DR

This study used Suzaku observations to analyze the X-ray spectral variability of Centaurus A, revealing a complex absorption structure, a variable reflection component, and potential jet-related emission, advancing understanding of active radio galaxy behavior.

Contribution

First detection of a partial covering Compton-thick absorber in Cen A, providing new insights into its X-ray spectral variability and jet contribution.

Findings

Identified a variable partial covering absorber in Cen A.

Detected a hard X-ray component possibly linked to jet emission.

Observed increased Fe-K line intensity correlating with flux changes.

Abstract

We observed a nearby radio galaxy, the Centaurus A (Cen A), three times with Suzaku in 2009, and measured the wide-band X-ray spectral variability more accurately than the previous measurements. The Cen A was in the active phase in 2009, and the flux became higher by a factor of 1.5--2.0 and the spectrum became harder than that in 2005. The Fe-K line intensity increased by 20--30% from 2005 to 2009. The correlation of the count rate between the XIS 3--8 keV and PIN 15--40 keV band showed a complex behavior with a deviation from a linear relation. The wide-band X-ray continuum in 2--200 keV can be fitted with an absorbed powerlaw model plus a reflection component, or a powerlaw with a partial covering Compton-thick absorption. The difference spectra between high and low flux periods in each observation were reproduced by a powerlaw with a partial covering Compton-thick absorption. Such a Compton-thick partial covering absorber was for the first time observed for the Cen A. The powerlaw photon index of the difference spectra in 2009 is almost the same as that of the time-averaged spectra in 2005, but steeper by $\sim0.2$ than that of the time-averaged spectra in 2009. This suggests an additional hard powerlaw component with a photon index of $<1.6$ in 2009. This hard component could be a lower part of the inverse-Compton-scattered component from the jet, whose gamma-ray emission has recently been detected with the Fermi/LAT.