Evidence for a cool disk and inhomogeneous coronae from wide-band temporal spectroscopy of cygnus X-1 with suzaku

Shin'ya Yamada, Kazuo Makishima, Chris Done, Shunsuke Torii, Hirofumi Noda, Soki Sakurai

Research output: Contribution to journalArticlepeer-review

39 Citations (Scopus)


Unified X-ray spectral and timing studies of Cygnus X-1 in the low/hard and hard intermediate state were conducted in a model-independent manner, using broadband Suzaku data acquired on 25 occasions from 2005 to 2009 with a total exposure of ̃450 ks. The unabsorbed 0.1-500 keV source luminosity changed over 0.8%-2.8% of the Eddington limit for 14.8 solar masses. Variations on short (1-2 seconds) and long (days to months) time scales require at least three separate components: a constant component localized below ̃2 keV, a broad soft one dominating in the 2-10 keV range, and a hard one mostly seen in the 10-300 keV range. In view of the truncated disk/hot inner-flow picture, these are respectively interpreted as emission from the truncated cool disk, a soft Compton component, and a hard Compton component. Long-term spectral evolution can be produced by the constant disk increasing in temperature and luminosity as the truncation radius decreases. The soft Compton component likewise increases, but the hard Compton does not, so that the spectrum in the hard intermediate state is dominated by the soft Compton component; on the other hand, the hard Compton component dominates the spectrum in the dim low/hard state, probably associated with a variable soft emission providing seed photons for the Comptonization.

Original languageEnglish
Article number80
JournalPublications of the Astronomical Society of Japan
Issue number4
Publication statusPublished - 2013 Aug 25
Externally publishedYes


  • Accretion
  • Accretion disk
  • Black hole physics
  • Stars: individual (Cygnus X-1)
  • X-ray: binaries

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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