Suzaku Results on Cygnus X-1 in the Low/Hard State

Abstract

The black-hole binary Cygnus X-1 was observed for 17 ks with the Suzaku X-ray observatory in 2005 October, while it was in a low/hard state with a 0.7-300 keV luminosity of 4.6 x 10^37 erg/s. The XIS and HXD spectra, spanning 0.7-400 keV, were reproduced successfully incorporating a cool accretion disk and a hot Comptonizing corona. The corona is characterized by an electron temperature of ~100 keV, and two optical depths of ~0.4 and ~1.5 which account for the harder and softer continua, respectively. The disk has the innermost temperature of ~0.2 keV, and is thought to protrude half way into the corona. The disk not only provides seed photons to the Compton cloud, but also produces a soft spectral excess, a mild reflection hump, and a weakly broadened iron line. A comparison with the Suzaku data on GRO J1655-40 reveals several interesting spectral differences, which can mostly be attributed to inclination effects assuming that the disk has a flat geometry while the corona is grossly spherical. An intensity-sorted spectroscopy indicates that the continuum becomes less Comptonized when the source flares up on times scales of 1-200 s, while the underlying disk remains unchanged.

21 pages, 12 figures, accepted for Publications of the Astronomical Society of Japan

References in corpus (10)

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• The Inclination Angle of and Mass of the Black Hole in XTE J1118+480
• In Orbit Timing Calibration of the Hard X-Ray Detector on Board Suzaku
• Low/Hard State Spectra of GRO J1655-40 Observed with Suzaku
• A Short Review of Relativistic Iron Lines from Stellar-Mass Black Holes

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