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1999MNRAS.309..496G - Mon. Not. R. Astron. Soc., 309, 496-512 (1999/October-3)
Radiation mechanisms and geometry of Cygnus X-1 in the soft state.
GIERLINSKI M., ZDZIARSKI A.A., POUTANEN J., COPPI P.S., EBISAWA K. and JOHNSON W.N.
Abstract (from CDS):
We model the soft component by multicolour blackbody disc emission taking into account the torque-free inner-boundary condition. If the disc extends down to the minimum stable orbit, the ASCARXTE data yield the most probable black hole mass of MX~10M☉ and an accretion rate, M{dot}~0.5LEc2, locating Cyg X-1 in the soft state in the upper part of the stable, gas-pressure-dominated, accretion-disc solution branch.
The spectrum of the corona is well modelled by repeated Compton scattering of seed photons from the disc off electrons with a hybrid, thermal/non-thermal distribution. The electron distribution can be characterized by a Maxwellian with an equilibrium temperature of kTe∼30-50keV, a Thomson optical depth of τ∼0.3 and a quasi-power-law tail. The compactness of the corona is 2≲ℓh≲7, and a presence of a significant population of electron-positron pairs is ruled out.
We find strong signatures of Compton reflection from a cold and ionized medium, presumably an accretion disc, with an apparent reflector solid angle, Ω/2π∼0.5-0.7. The reflected continuum is accompanied by a broad iron Kα line.
Abstract Copyright: 1999, Royal Astronomical Society
Journal keyword(s): accretion, accretion discs - radiation mechanisms: non-thermal - stars: individual: Cygnus X-1 - gamma-rays: observations - gamma-rays: theory - X-rays: stars
Simbad objects: 3
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