On the accretion geometry of Cyg X-1 in the low/hard state

We fit the broad-band RXTE PCA and HEXTE spectrum of Cyg X-1 from 3–200 keV with reflection models which calculate the vertical ionization structure of an X-ray illuminated disc. We consider two geometries corresponding to a truncated disc/inner hot flow and magnetic flares above an untruncated disc...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2003-06, Vol.342 (2), p.557-563
Main Authors: Barrio, F. Eugenio, Done, Chris, Nayakshin, Sergei
Format: Article
Language:English
Subjects:
accretion
accretion discs
accretion, accretion discs
black hole physics
stars: individual: Cygnus X-1
X-rays: binaries
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Summary:We fit the broad-band RXTE PCA and HEXTE spectrum of Cyg X-1 from 3–200 keV with reflection models which calculate the vertical ionization structure of an X-ray illuminated disc. We consider two geometries corresponding to a truncated disc/inner hot flow and magnetic flares above an untruncated disc. Both models are able to fit the PCA 3–20 keV data, but with very different spectral components. In the magnetic flare models the 3–20 keV PCA spectrum contains a large amount of highly ionized reflection, while in the truncated disc models the amount of reflection is rather small. The Compton downscattering rollover in reflected emission means that the magnetic flare models predict a break in the spectrum at the high energies covered by the HEXTE bandpass which is not seen. By contrast, the weakly illuminated truncated disc models can easily fit the 3–200 keV spectra.
ISSN:0035-8711
1365-2966
DOI:10.1046/j.1365-8711.2003.06555.x