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Publications of the Astronomical Society of Japan 61, SP. 1 (2009) S299-S316
X-Ray Spectral Variability of the Seyfert Galaxy NGC 4051 Observed with Suzaku
Y. Terashima, L. C. Gallo, H. Inoue, A. G. Markowitz, J. N. Reeves, N. Anabuki, A. C. Fabian, R. E. Griffiths, K. Hayashida, T. Itoh, N. Kokubun, A. Kubota, G. Miniutti1, T. Takahashi, M. Yamauchi, D. Yonetoku
(2009)

We report on results from a Suzaku observation of the narrow-line Seyfert 1 NGC 4051. During our observation, large-amplitude rapid variability was seen, and the averaged 2-10keV flux was 8.1$\times$10$^{-12}$ergs$^{-1}$cm$^{-2}$, which is several times lower than the historical average. The X-ray spectrum hardens when the source flux becomes lower, confirming the trend of spectral variability known for many Seyfert 1 galaxies. The broad-band averaged spectrum and spectra in high- and low-flux intervals were analyzed. The spectra were first fitted with a model consisting of a power-law component, a reflection continuum originating in cold matter, a blackbody component, two zones of ionized absorber, and several Gaussian emission lines. The amount of reflection is rather large ($R$ $\sim$ 7, where $R$ $=$ 1 corresponds to reflection by an infinite slab), while the equivalent width of the Fe-K line at 6.4keV is modest (140eV) for the averaged spectrum. We then modeled the overall spectra by introducing partial covering for the power-law component and reflection continuum independently. The column density for the former is 1$\times$10$^{23}$cm$^{-2}$, while it is fixed at 1$\times$10$^{24}$cm$^{-2}$ for the latter. By comparing the spectra in different flux states, we could identify the causes of spectral variability.
1 :  APC - UMR 7164 - AstroParticule et Cosmologie
APC - AHE
Physique/Astrophysique/Cosmologie et astrophysique extra-galactique

Planète et Univers/Astrophysique/Cosmologie et astrophysique extra-galactique
galaxies: active – galaxies: individual (NGC 4051) – X-rays: galaxies
Lien vers le texte intégral : 
http://fr.arXiv.org/abs/0811.0692