TY - JOUR
T1 - ASCA observation of cygnus X-l in the soft state
T2 - Mass of the compact object
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
PY - 1997
Y1 - 1997
N2 - 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.
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.
KW - Stars: individual (Cygnus X-1)
KW - X-rays: general
KW - X-rays: stars
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U2 - 10.1086/310816
DO - 10.1086/310816
M3 - Article
AN - SCOPUS:21744453018
SN - 0004-637X
VL - 485
SP - L87-L90
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2 PART II
ER -