Highly ionized Fe-K absorption line from Cygnus X-1 in the high/soft state observed with Suzaku

S. Yamada, S. Torii, S. Mineshige, Y. Ueda, A. Kubota, P. Gandhi, C. Done, H. Noda, A. Yoshikawa, K. Makishima

研究成果: Article査読

9 被引用数 (Scopus)

抄録

We present observations of a transient He-like Fe Kα absorption line in Suzaku observations of the black hole binary Cygnus X-1 on 2011 October 5 near superior conjunction during the high/soft state, which enable us to map the full evolution from the start to the end of the episodic accretion phenomena or dips for the first time. We model the X-ray spectra during the event and trace their evolution. The absorption line is rather weak in the first half of the observation, but instantly deepens for ≃10 ks, and weakens thereafter. The overall change in equivalent width is a factor of ≃3, peaking at an orbital phase of ≃0.08. This is evidence that the companion stellar wind feeding the black hole is clumpy. By analyzing the line with a Voigt profile, it is found to be consistent with a slightly redshifted Fe XXV transition, or possibly a mixture of several species less ionized than Fe XXV. The data may be explained by a clump located at a distance of ≃1010-12 cm with a density of ≃10(- 13)-(- 11) g cm-3, which accretes onto and/or transits the line of sight to the black hole, causing an instant decrease in the observed degree of ionization and/or an increase in density of the accreting matter. Continued monitoring for individual events with future X-ray calorimeter missions such as ASTRO-H and AXSIO will allow us to map out the accretion environment in detail and how it changes between the various accretion states.

本文言語English
論文番号L35
ジャーナルAstrophysical Journal Letters
767
2
DOI
出版ステータスPublished - 2013 4 20

ASJC Scopus subject areas

  • 天文学と天体物理学
  • 宇宙惑星科学

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