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

Fukazawa Yasushi

Hiragi Kazuyoshi

Yamazaki Syoko

Mizuno Motohiro

Hayashi Kazuma

Hayashi Katsuhiro

Nishino Sho

Takahashi Hiromitsu

Ohno Masanori

The Astrophysical Journal

We observed a nearby radio galaxy, Centaurus A (Cen A), three times with Suzaku in 2009 and measured the wide-band X-ray spectral variability more accurately than previous measurements. The Cen A was in an 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 power-law model plus a reflection component, or a power law with a partial covering Compton-thick absorption. The difference spectra between high and low flux periods in each observation were reproduced by a power law with a partial covering Compton-thick absorption. Such a Compton-thick partial covering absorber was observed for the first time in Cen A. The power-law photon index of the difference spectra in 2009 is almost the same as that of the time-averaged spectra in 2005, but steeper by similar to 0.2 than that of the time-averaged spectra in 2009. This suggests an additional hard power-law 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 Large Area Telescope.

galaxies: active

galaxies: individual (Centaurus A)

galaxies: Seyfert

X-rays: galaxies

天文学・宇宙科学 [ 440 ]

英語

IOP Publishing Ltd

(c) 2011. The American Astronomical Society. All rights reserved.

[ISSN] 0004-637X

[DOI] 10.1088/0004-637X/743/2/124

[NCID] AA00553242

[DOI] http://dx.doi.org/10.1088/0004-637X/743/2/124