A complete relativistic ionized accretion disc in Cygnus X-1 |
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| Authors: | AJ Young † AC Fabian RR Ross Y Tanaka |
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| Institution: | 1Institute of Astronomy, Madingley Road, Cambridge CB3 0HA;2Department of Physics, College of the Holy Cross, Worcester, MA 01610, USA;3Max-Planck-Institut für extraterrestriche Physik, D-85740 Garching, Germany |
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| Abstract: | The galactic black hole candidate Cygnus X-1 is observed to be in one of two X-ray spectral states: either the low/hard (low soft X-ray flux and a flat power-law tail) or high/soft (high blackbody-like soft X-ray flux and a steep power-law tail) state. The physical origin of these two states is unclear. We present here a model of an ionized accretion disc, the spectrum of which is blurred by relativistic effects, and fit it to the ASCA , Ginga and EXOSAT data of Cygnus X-1 in both spectral states. We confirm that relativistic blurring provides a much better fit to the low/hard state data and, contrary to some previous results, find the data of both states to be consistent with an ionized thin accretion disc with a reflected fraction of unity extending to the innermost stable circular orbit around the black hole. Our model is an alternative to those that, in the low/hard state, require the accretion disc to be truncated at a few tens of Schwarzschild radii, within which there is a Thomson-thin, hot accretion flow. We suggest a mechanism that may cause the changes in spectral state. |
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| Keywords: | accretion accretion discs black hole physics binaries: close stars: individual: Cyg X-1 X-rays: general X-rays: stars |
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