N. Kokubun

Japan Aerospace Exploration Agency, Chōfu, Tokyo-to, Japan

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Publications (1)2.07 Total impact

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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.
    Publications- Astronomical Society of Japan 12/2008; 61(sp1). DOI:10.1093/pasj/61.sp1.S299 · 2.07 Impact Factor

Publication Stats

18 Citations
2.07 Total Impact Points


  • 2008
    • Japan Aerospace Exploration Agency
      • Institute of Space and Astronautical Science (ISAS)
      Chōfu, Tokyo-to, Japan