X-Ray spectral variability of the seyfert galaxy NGC 4051 observed with Suzaku

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

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27 Citations (Scopus)


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 × 10-12ergs-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 ̃ 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 (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 × 10 23 cm-2, while it is fixed at 1 x 1024cm -2 for the latter. By comparing the spectra in different flux states, we could identify the causes of spectral variability.

Original languageEnglish
Pages (from-to)S299-S316
JournalPublications of the Astronomical Society of Japan
Issue numberSUPPL. 1
Publication statusPublished - 2009


  • Galaxies: Active
  • Galaxies: Individual (NGC 4051)
  • X-rays: Galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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