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Yuichi Terashima, Luigi C. Gallo, Hirohiko Inoue, Alex G. Markowitz, James N. Reeves, Naohisa Anabuki, Andrew C. Fabian, Richard E. Griffiths, Kiyoshi Hayashida, Takeshi Itoh, Norihide Kokubun, Aya Kubota, Giovanni Miniutti, Tadayuki Takahashi, Makoto Yamauchi, Daisuke Yonetoku, X-Ray Spectral Variability of the Seyfert Galaxy NGC 4051 Observed with Suzaku, Publications of the Astronomical Society of Japan, Volume 61, Issue sp1, 30 January 2009, Pages S299–S316, https://doi.org/10.1093/pasj/61.sp1.S299
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Abstract
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 2–10 keV flux was 8.1|$\times$|10|$^{-12}$|erg s|$^{-1}$|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 6.4 keV is modest (140 eV) 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.
