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Preprint B/11

Vertical structure of the outer accretion disk in persistent low-mass X-ray binaries

Mescheryakov, A. V. (1), Shakura, N. I. (2), Suleimanov, V. F. (3,4)

(1) Space Research Institute, Russian Academy of Sciences
(2) Moscow State University
(3) Institute for Astronomy and Astrophysics, University of Tübingen, Germany
(4) Kazan Federal University, Russia

Astronomy Letters 37 (2011), 311

Abstract. We have investigated the influence of X-ray irradiation on the vertical structure of the outer accretion disk in low-mass X-ray binaries by performing a self-consistent calculation of the vertical structure and X-ray radiation transfer in the disk. Penetrating deep into the disk, the field of scattered X-ray photons with energy E ≥ 10 keV exerts a significant influence on the vertical structure of the accretion disk at a distance R ≥ 10¹⁰ cm from the neutron star. At a distance R ~ 10¹¹ cm, where the total surface density in the disk reaches Sigma₀ ~ 20 g cm^-2, X-ray heating affects all layers of an optically thick disk. The X-ray heating effect is enhanced significantly in the presence of an extended atmospheric layer with a temperature T_atm ≈ (2-3) x 10⁶ K above the accretion disk. We have derived simple analytic formulas for the disk heating by scattered X-ray photons using an approximate solution of the transfer equation by the Sobolev method. This approximation has a ≲10% accuracy in the range of X-ray photon energies E < 20 keV.
 
Key words: low-mass X-ray binaries, accretion disks

Astrophysics (astro-ph): 1108.4222

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