Suzaku results on cygnus X-1 in the low/hard State

Kazuo Makishima, Hiromitsu Takahashi, Shin'ya Yamada, Chris Done, Aya Kubota, Tadayasu Dotani, Ken Ebisawa, Takeshi Itoh, Shunji Kitamoto, Hitoshi Negoro, Yoshihiro Ueda, Kazutaka Yamaoka

研究成果: Article

91 引用 (Scopus)


The black-hole binary Cygnus X-1 was observed for 17 ks with the Suzaku X-ray observatory in 2005 October, while it was in a low/hard state with a 0.7-300keV luminosity of 4.6 × 1037 erg s-1. The XIS and HXD spectra, spanning 0.7-400 keV, were reproduced successfully, incorporating a cool accretion disk and a hot Comptonizing corona. The corona is characterized by an electron temperature of ∼ 100 keV, and two optical depths of ∼0.4 and ∼ 1.5, which account for the softer and harder continua, respectively. The disk has an innermost temperature of ∼ 0.2keV, and is thought to protrude half way into the corona. The disk not only provides seed photons to the Compton cloud, but also produces a soft spectral excess, a mild reflection hump, and a weakly broadened iron line. A comparison with the Suzaku data on GRO J1655-40 reveals several interesting spectral differences, which can mostly be attributed to inclination effects, assuming that the disk has a flat geometry while the corona is grossly spherical. An intensity-sorted spectroscopy indicates that the continuum becomes less Comptonized when the source flares up on time scales of 1-200 s, while the underlying disk remains unchanged.

ジャーナルPublications of the Astronomical Society of Japan
出版物ステータスPublished - 2008 1 1

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Makishima, K., Takahashi, H., Yamada, S., Done, C., Kubota, A., Dotani, T., Ebisawa, K., Itoh, T., Kitamoto, S., Negoro, H., Ueda, Y., & Yamaoka, K. (2008). Suzaku results on cygnus X-1 in the low/hard State. Publications of the Astronomical Society of Japan, 60(3), 585-604.