ASCA observation of cygnus X-l in the soft state

Mass of the compact object

Tadayasu Dotani, Hajime Inoue, Kazuhisa Mitsuda, Fumiaki Nagase, Hitoshi Negoro, Yoshihiro Ueda, Kazuo Makishima, Aya Kubota, Ken Ebisawa, Yasuo Tanaka

Research output: Contribution to journalArticle

52 Citations (Scopus)

Abstract

We describe the ASCA observation of the black hole candidate Cyg X-l in the soft state of 1996 May and report the mass estimation of the central object from X-ray spectral analysis. The energy spectrum in 0.7-10 keV can be described by the sum of a power law (F = 2.3 ± 0.1) and an ultrasoft component; the latter is most probably the emission from an optically thick accretion disk. Through the spectral analysis of the ultrasoft component, we estimated the size of the accretion disk, which is closely related to the Schwarzschild radius and, hence, to the mass of the central object. Taking the general relativistic effects into account, the most probable mass of the compact object is estimated as 12-1+3M. This value is independent of, yet consistent with, the mass estimate based on the orbital kinematics information.

Original languageEnglish
JournalAstrophysical Journal
Volume485
Issue number2 PART II
Publication statusPublished - 1997
Externally publishedYes

Fingerprint

accretion disks
spectral analysis
spectrum analysis
accretion
relativistic effects
power law
energy spectra
kinematics
orbitals
radii
estimates
energy
x rays
effect

Keywords

  • Stars: individual (Cygnus X-1)
  • X-rays: general
  • X-rays: stars

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Dotani, T., Inoue, H., Mitsuda, K., Nagase, F., Negoro, H., Ueda, Y., ... Tanaka, Y. (1997). ASCA observation of cygnus X-l in the soft state: Mass of the compact object. Astrophysical Journal, 485(2 PART II).

ASCA observation of cygnus X-l in the soft state : Mass of the compact object. / Dotani, Tadayasu; Inoue, Hajime; Mitsuda, Kazuhisa; Nagase, Fumiaki; Negoro, Hitoshi; Ueda, Yoshihiro; Makishima, Kazuo; Kubota, Aya; Ebisawa, Ken; Tanaka, Yasuo.

In: Astrophysical Journal, Vol. 485, No. 2 PART II, 1997.

Research output: Contribution to journalArticle

Dotani, T, Inoue, H, Mitsuda, K, Nagase, F, Negoro, H, Ueda, Y, Makishima, K, Kubota, A, Ebisawa, K & Tanaka, Y 1997, 'ASCA observation of cygnus X-l in the soft state: Mass of the compact object', Astrophysical Journal, vol. 485, no. 2 PART II.
Dotani T, Inoue H, Mitsuda K, Nagase F, Negoro H, Ueda Y et al. ASCA observation of cygnus X-l in the soft state: Mass of the compact object. Astrophysical Journal. 1997;485(2 PART II).
Dotani, Tadayasu ; Inoue, Hajime ; Mitsuda, Kazuhisa ; Nagase, Fumiaki ; Negoro, Hitoshi ; Ueda, Yoshihiro ; Makishima, Kazuo ; Kubota, Aya ; Ebisawa, Ken ; Tanaka, Yasuo. / ASCA observation of cygnus X-l in the soft state : Mass of the compact object. In: Astrophysical Journal. 1997 ; Vol. 485, No. 2 PART II.
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AU - Dotani, Tadayasu

AU - Inoue, Hajime

AU - Mitsuda, Kazuhisa

AU - Nagase, Fumiaki

AU - Negoro, Hitoshi

AU - Ueda, Yoshihiro

AU - Makishima, Kazuo

AU - Kubota, Aya

AU - Ebisawa, Ken

AU - Tanaka, Yasuo

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AB - We describe the ASCA observation of the black hole candidate Cyg X-l in the soft state of 1996 May and report the mass estimation of the central object from X-ray spectral analysis. The energy spectrum in 0.7-10 keV can be described by the sum of a power law (F = 2.3 ± 0.1) and an ultrasoft component; the latter is most probably the emission from an optically thick accretion disk. Through the spectral analysis of the ultrasoft component, we estimated the size of the accretion disk, which is closely related to the Schwarzschild radius and, hence, to the mass of the central object. Taking the general relativistic effects into account, the most probable mass of the compact object is estimated as 12-1+3M⊙. This value is independent of, yet consistent with, the mass estimate based on the orbital kinematics information.

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