Simultaneous asca and rxte observations of cygnus x-1 during its 1996 state transition
Nov, 199711 pages
Published in:
- Astrophys.J.Lett. 493 (1998) L75
e-Print:
- astro-ph/9711164 [astro-ph]
DOI:
View in:
Citations per year
Abstract: (arXiv)
We report results from simultaneous ASCA and RXTE observations of Cyg 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, thus make it possible to disentangle various spectral components. The low-energy spectrum is dominated by an ultra-soft 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 re-emitted photons produce the observed ``reflection bump''. We show that the reflecting medium subtends only a small solid angle (), but has a large ionization parameter such that iron is ionized up to \ion{Fe}{24}-\ion{Fe}{26}. The presence of a broad iron line at 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 with a central corona surrounding the black hole and the reflection occurring in the innermost region of the disk where matter is highly ionized.References(22)
Figures(0)