Detailed spectral study of an ultra-luminous compact X-ray source, M 81 X-9, in the disk-dominated state

Naoko Tsunoda, Aya Kubota, Masaaki Namiki, Masahiko Sugiho, Kiyoshi Kawabata, Kazuo Makishima

研究成果: Article査読

23 被引用数 (Scopus)

抄録

We report on the results of detailed spectral studies of an ultra-luminous X-ray source (ULX), M 81 X-9 (Holmberg IX X-1), conducted with XMM-Newton on 2001 April 22 and with ASCA on 1999 April 6. On both occasions, the source showed an unabsorbed 0.5-10keV luminosity of ∼2 × 1040 erg s-1 (assuming a distance of 3.4 Mpc) and a soft spectrum, apparently represented by a multi-color disk model with an innermost disk temperature of 1.3-1.5 keV. Adding a power-law model further improved the fit. However, as previously reported, the high luminosity cannot be reconciled with the high disk temperature within the framework of the standard accretion disk radiating at a sub-Eddington luminosity. Therefore, we modified the multi-color disk model, and allowed the local disk temperature to scale as ∝ r-p on the distance r from the black hole, with p being a free parameter. We then found that the XMM-Newton and the ASCA spectra can be both successfully reproduced with p ∼ 0.6 and the innermost disk temperature of 1.4-1.8 keV. These flatter temperature profiles suggest a deviation from the standard Shakura-Sunyaev disk, and are consistent with predictions of a slim-disk model.

本文言語English
ページ(範囲)1081-1088
ページ数8
ジャーナルPublications of the Astronomical Society of Japan
58
6
DOI
出版ステータスPublished - 2006
外部発表はい

ASJC Scopus subject areas

  • 天文学と天体物理学
  • 宇宙惑星科学

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