Suzaku discovery of iron absorption lines in outburst spectra of the X-ray transient 4U 1630-472

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

Research output: Contribution to journalArticle

52 Citations (Scopus)

Abstract

We present the results of six Suzaku observations of the recurrent black hole transient 4U 1630-472 during its decline from outburst from February 8 to March 23 in 2006. All observations show the typical high/soft state spectral shape in the 2-50 keV band, roughly described by an optically thick-disk spectrum in the soft energy band plus a weak power-law tail that becomes dominant only above ∼ 20keV. The disk temperature decreases from 1.4keV to 1.2 keV as the flux decreases by a factor of 2, consistent with a constant radius, as expected for disk-dominated spectra. All of the observations reveal significant absorption lines from highly ionized (H-like and He-like) iron Kα's at 7.0 keV and 6.7 keV. The energies of these absorption lines suggest a blue shift with an outflow velocity of ∼ 1000 ms-1. The H-like iron Kα equivalent width remains approximately constant at ∼ 30 eV over all of the observations, while that of the He-like Kα line increases from 7 eV to 20 eV. Thus, the ionization state of the material decreases, as expected from the decline in flux. By fitting the profile with Voigt functions (curve of growth) together with detailed photo-ionization calculations, the total absorbing column, and the ionization parameter were estimated to be (1.0-0.7) × 1023 cm-2 and (6-4) × 104, respectively, for a velocity dispersion of 500km s -1. This in turn constrains the size of the plasma to be ∼ 1010 cm, assuming a source distance of 10 kpc.

Original languageEnglish
JournalPublications of the Astronomical Society of Japan
Volume59
Issue number1 SPEC. ISS.
Publication statusPublished - 2007
Externally publishedYes

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outburst
ionization
iron
x rays
K lines
energy
power law
outflow
blue shift
energy bands
photoionization
plasma
radii
curves
profiles
temperature
parameter
material
calculation

Keywords

  • Accretion, accretion disks
  • X-rays: individual (4U 1630-472)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Kubota, A., Dotani, T., Cottam, J., Kotani, T., Done, C., Ueda, Y., ... Angelini, L. (2007). Suzaku discovery of iron absorption lines in outburst spectra of the X-ray transient 4U 1630-472. Publications of the Astronomical Society of Japan, 59(1 SPEC. ISS.).

Suzaku discovery of iron absorption lines in outburst spectra of the X-ray transient 4U 1630-472. / Kubota, Aya; Dotani, Tadayasu; Cottam, Jean; Kotani, Taro; Done, Chris; Ueda, Yoshihiro; Fabian, Andrew C.; Yasuda, Tomonori; Takahashi, Hiromitsu; Fukazawa, Yasushi; Yamaoka, Kazutaka; Makishima, Kazuo; Yamada, Shinya; Kohmura, Takayoshi; Angelini, Lorella.

In: Publications of the Astronomical Society of Japan, Vol. 59, No. 1 SPEC. ISS., 2007.

Research output: Contribution to journalArticle

Kubota, A, Dotani, T, Cottam, J, Kotani, T, Done, C, Ueda, Y, Fabian, AC, Yasuda, T, Takahashi, H, Fukazawa, Y, Yamaoka, K, Makishima, K, Yamada, S, Kohmura, T & Angelini, L 2007, 'Suzaku discovery of iron absorption lines in outburst spectra of the X-ray transient 4U 1630-472', Publications of the Astronomical Society of Japan, vol. 59, no. 1 SPEC. ISS..
Kubota, Aya ; Dotani, Tadayasu ; Cottam, Jean ; Kotani, Taro ; Done, Chris ; Ueda, Yoshihiro ; Fabian, Andrew C. ; Yasuda, Tomonori ; Takahashi, Hiromitsu ; Fukazawa, Yasushi ; Yamaoka, Kazutaka ; Makishima, Kazuo ; Yamada, Shinya ; Kohmura, Takayoshi ; Angelini, Lorella. / Suzaku discovery of iron absorption lines in outburst spectra of the X-ray transient 4U 1630-472. In: Publications of the Astronomical Society of Japan. 2007 ; Vol. 59, No. 1 SPEC. ISS.
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abstract = "We present the results of six Suzaku observations of the recurrent black hole transient 4U 1630-472 during its decline from outburst from February 8 to March 23 in 2006. All observations show the typical high/soft state spectral shape in the 2-50 keV band, roughly described by an optically thick-disk spectrum in the soft energy band plus a weak power-law tail that becomes dominant only above ∼ 20keV. The disk temperature decreases from 1.4keV to 1.2 keV as the flux decreases by a factor of 2, consistent with a constant radius, as expected for disk-dominated spectra. All of the observations reveal significant absorption lines from highly ionized (H-like and He-like) iron Kα's at 7.0 keV and 6.7 keV. The energies of these absorption lines suggest a blue shift with an outflow velocity of ∼ 1000 ms-1. The H-like iron Kα equivalent width remains approximately constant at ∼ 30 eV over all of the observations, while that of the He-like Kα line increases from 7 eV to 20 eV. Thus, the ionization state of the material decreases, as expected from the decline in flux. By fitting the profile with Voigt functions (curve of growth) together with detailed photo-ionization calculations, the total absorbing column, and the ionization parameter were estimated to be (1.0-0.7) × 1023 cm-2 and (6-4) × 104, respectively, for a velocity dispersion of 500km s -1. This in turn constrains the size of the plasma to be ∼ 1010 cm, assuming a source distance of 10 kpc.",
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AU - Kubota, Aya

AU - Dotani, Tadayasu

AU - Cottam, Jean

AU - Kotani, Taro

AU - Done, Chris

AU - Ueda, Yoshihiro

AU - Fabian, Andrew C.

AU - Yasuda, Tomonori

AU - Takahashi, Hiromitsu

AU - Fukazawa, Yasushi

AU - Yamaoka, Kazutaka

AU - Makishima, Kazuo

AU - Yamada, Shinya

AU - Kohmura, Takayoshi

AU - Angelini, Lorella

PY - 2007

Y1 - 2007

N2 - We present the results of six Suzaku observations of the recurrent black hole transient 4U 1630-472 during its decline from outburst from February 8 to March 23 in 2006. All observations show the typical high/soft state spectral shape in the 2-50 keV band, roughly described by an optically thick-disk spectrum in the soft energy band plus a weak power-law tail that becomes dominant only above ∼ 20keV. The disk temperature decreases from 1.4keV to 1.2 keV as the flux decreases by a factor of 2, consistent with a constant radius, as expected for disk-dominated spectra. All of the observations reveal significant absorption lines from highly ionized (H-like and He-like) iron Kα's at 7.0 keV and 6.7 keV. The energies of these absorption lines suggest a blue shift with an outflow velocity of ∼ 1000 ms-1. The H-like iron Kα equivalent width remains approximately constant at ∼ 30 eV over all of the observations, while that of the He-like Kα line increases from 7 eV to 20 eV. Thus, the ionization state of the material decreases, as expected from the decline in flux. By fitting the profile with Voigt functions (curve of growth) together with detailed photo-ionization calculations, the total absorbing column, and the ionization parameter were estimated to be (1.0-0.7) × 1023 cm-2 and (6-4) × 104, respectively, for a velocity dispersion of 500km s -1. This in turn constrains the size of the plasma to be ∼ 1010 cm, assuming a source distance of 10 kpc.

AB - We present the results of six Suzaku observations of the recurrent black hole transient 4U 1630-472 during its decline from outburst from February 8 to March 23 in 2006. All observations show the typical high/soft state spectral shape in the 2-50 keV band, roughly described by an optically thick-disk spectrum in the soft energy band plus a weak power-law tail that becomes dominant only above ∼ 20keV. The disk temperature decreases from 1.4keV to 1.2 keV as the flux decreases by a factor of 2, consistent with a constant radius, as expected for disk-dominated spectra. All of the observations reveal significant absorption lines from highly ionized (H-like and He-like) iron Kα's at 7.0 keV and 6.7 keV. The energies of these absorption lines suggest a blue shift with an outflow velocity of ∼ 1000 ms-1. The H-like iron Kα equivalent width remains approximately constant at ∼ 30 eV over all of the observations, while that of the He-like Kα line increases from 7 eV to 20 eV. Thus, the ionization state of the material decreases, as expected from the decline in flux. By fitting the profile with Voigt functions (curve of growth) together with detailed photo-ionization calculations, the total absorbing column, and the ionization parameter were estimated to be (1.0-0.7) × 1023 cm-2 and (6-4) × 104, respectively, for a velocity dispersion of 500km s -1. This in turn constrains the size of the plasma to be ∼ 1010 cm, assuming a source distance of 10 kpc.

KW - Accretion, accretion disks

KW - X-rays: individual (4U 1630-472)

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