Simultaneous ASCA and RXTE observations of Cygnus X-l during its 1996 state transition

Wei Cui, K. Ebisawa, T. Dotani, Aya Kubota

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

We report results from simultaneous ASCA and RXTE observations of Cygnus X-1 when the source made a rare transition from the hard (=low) state to the soft (=high) state in 1996. These observations together cover a broad energy range ∼0.7-50 keV with a moderate energy resolution at the iron K band and thus make it possible to disentangle various spectral components. The low-energy spectrum is dominated by an ultrasoft component, which is likely to be the emission from the hottest inner portion of the accretion disk around the black hole. At high energies, the X-ray spectrum can be described by a Comptonized spectrum with a reflection component. The Compton corona, which upscatters soft "seed photons" to produce the hard X-ray emission, is found to have a y-parameter ∼0.28. The hard X-ray emission illuminates the accretion disk, and the reemitted photons produce the observed "reflection bump." We show that the reflecting medium subtends only a small solid angle (∼0.15 × 2π) but has a large ionization parameter such that iron is ionized up to Fe xxiv-Fe xxvi. The presence of a broad iron line at 6.58 ± 0.04 keV is also consistent with a highly ionized disk, if we take into account the gravitational and Doppler shift of the line energy. These results imply a geometry of a central corona surrounding the black hole and the reflection occurring in the innermost region of the disk where matter is highly ionized.

Original languageEnglish
JournalAstrophysical Journal
Volume493
Issue number2 PART II
Publication statusPublished - 1998
Externally publishedYes

Fingerprint

X Ray Timing Explorer
iron
accretion disks
coronas
energy
corona
x rays
accretion
photons
extremely high frequencies
seeds
energy spectra
ionization
shift
seed
geometry
parameter

Keywords

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

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Simultaneous ASCA and RXTE observations of Cygnus X-l during its 1996 state transition. / Cui, Wei; Ebisawa, K.; Dotani, T.; Kubota, Aya.

In: Astrophysical Journal, Vol. 493, No. 2 PART II, 1998.

Research output: Contribution to journalArticle

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abstract = "We report results from simultaneous ASCA and RXTE observations of Cygnus X-1 when the source made a rare transition from the hard (=low) state to the soft (=high) state in 1996. These observations together cover a broad energy range ∼0.7-50 keV with a moderate energy resolution at the iron K band and thus make it possible to disentangle various spectral components. The low-energy spectrum is dominated by an ultrasoft component, which is likely to be the emission from the hottest inner portion of the accretion disk around the black hole. At high energies, the X-ray spectrum can be described by a Comptonized spectrum with a reflection component. The Compton corona, which upscatters soft {"}seed photons{"} to produce the hard X-ray emission, is found to have a y-parameter ∼0.28. The hard X-ray emission illuminates the accretion disk, and the reemitted photons produce the observed {"}reflection bump.{"} We show that the reflecting medium subtends only a small solid angle (∼0.15 × 2π) but has a large ionization parameter such that iron is ionized up to Fe xxiv-Fe xxvi. The presence of a broad iron line at 6.58 ± 0.04 keV is also consistent with a highly ionized disk, if we take into account the gravitational and Doppler shift of the line energy. These results imply a geometry of a central corona surrounding the black hole and the reflection occurring in the innermost region of the disk where matter is highly ionized.",
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T1 - Simultaneous ASCA and RXTE observations of Cygnus X-l during its 1996 state transition

AU - Cui, Wei

AU - Ebisawa, K.

AU - Dotani, T.

AU - Kubota, Aya

PY - 1998

Y1 - 1998

N2 - We report results from simultaneous ASCA and RXTE observations of Cygnus X-1 when the source made a rare transition from the hard (=low) state to the soft (=high) state in 1996. These observations together cover a broad energy range ∼0.7-50 keV with a moderate energy resolution at the iron K band and thus make it possible to disentangle various spectral components. The low-energy spectrum is dominated by an ultrasoft component, which is likely to be the emission from the hottest inner portion of the accretion disk around the black hole. At high energies, the X-ray spectrum can be described by a Comptonized spectrum with a reflection component. The Compton corona, which upscatters soft "seed photons" to produce the hard X-ray emission, is found to have a y-parameter ∼0.28. The hard X-ray emission illuminates the accretion disk, and the reemitted photons produce the observed "reflection bump." We show that the reflecting medium subtends only a small solid angle (∼0.15 × 2π) but has a large ionization parameter such that iron is ionized up to Fe xxiv-Fe xxvi. The presence of a broad iron line at 6.58 ± 0.04 keV is also consistent with a highly ionized disk, if we take into account the gravitational and Doppler shift of the line energy. These results imply a geometry of a central corona surrounding the black hole and the reflection occurring in the innermost region of the disk where matter is highly ionized.

AB - We report results from simultaneous ASCA and RXTE observations of Cygnus X-1 when the source made a rare transition from the hard (=low) state to the soft (=high) state in 1996. These observations together cover a broad energy range ∼0.7-50 keV with a moderate energy resolution at the iron K band and thus make it possible to disentangle various spectral components. The low-energy spectrum is dominated by an ultrasoft component, which is likely to be the emission from the hottest inner portion of the accretion disk around the black hole. At high energies, the X-ray spectrum can be described by a Comptonized spectrum with a reflection component. The Compton corona, which upscatters soft "seed photons" to produce the hard X-ray emission, is found to have a y-parameter ∼0.28. The hard X-ray emission illuminates the accretion disk, and the reemitted photons produce the observed "reflection bump." We show that the reflecting medium subtends only a small solid angle (∼0.15 × 2π) but has a large ionization parameter such that iron is ionized up to Fe xxiv-Fe xxvi. The presence of a broad iron line at 6.58 ± 0.04 keV is also consistent with a highly ionized disk, if we take into account the gravitational and Doppler shift of the line energy. These results imply a geometry of a central corona surrounding the black hole and the reflection occurring in the innermost region of the disk where matter is highly ionized.

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