• Fukazawa, Yasushi
• Yasuda, Tomonori
• Fabian, Andy C.
• Ueda, Yoshihiro
• Kotani, Taro
• Cottam, Jean
• Team, Suzaku
• Takahashi, Hiromitsu
• Yamaoka, Kazutaka
• Angelini, Lorella
• Kohmura, Takayoshi
• Yamada, Shinya
• Dotani, Tadayasu
• Kubota, Aya
• Done, Chris
• Makishima, Kazuo

Abstract

An outburst of the black hole transient 4U1630-472 was reported by the RXTE All Sky Monitor on 2005 December. From 2006 February 8 to March 23, we observed this source six times with each exposure of 21-23ks as part of the initial performance verification of Suzaku. Suzaku carries 4 sets of X-ray telescopes each with a focal-plane X-ray CCD camera (XIS, X-ray Imaging Spectrometer), together with a non-imaging Hard X-ray Detector (HXD) which covers the 10--600 keV energy band with the Si PIN photo-diodes and the GSO scintillation counters. During the observations in 2 months, the source signal was clearly detected up to 40keV with PIN, and its spectrum was found to bethe typical high/soft state with the dominant disk component and very weak hard tail of photon index ̃2.5. Based on the XIS spectra, the disk temperature was found to be 1.4keV at the first observation and gradually decreased to 1.2keV by keeping disk inner radius constant at ̃25km (distance and inclination are assumed to be 10kpc and 70 degree). Thus the bolometric disk luminosity changed from 2.8E38 erg/s to 1.6E38 erg/s. Importantly, with this Suzaku observation, we discovered narrow absorption lines at 6.7 keV and 7.0 keV, which correspond to H- and He-like iron K alpha, respectively. Through six observations, H-like iron K alpha was found to show almost constant equivalent width of 30eV, while the equivalent width of He-like iron K alpha increased from 8eV to 20 eV. The values of equivalent width correspond to iron column density of 1-4E17 /cm2 and 1E18/cm2 for He- and H-like iron, respectively, with an assumption of velocity dispersion of 500km/ s. We run xstar to have ratio of He- like to H-like iron for the disk spectra, and found that the xi-parameters should change from 5-7E4 to 3-4E4 from the first to the sixth observation. Based on these results, we will discuss geometry and origin of the absorption lines together with change of the accretion disk parameters....

Topics

• density
• dispersion
• iron