Vertical Structure of the Outer Accretion Disk in Persistent Low-Mass X-Ray Binaries

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 $E\gtrsim 10$\,keV exerts a significant influence on the vertical structure of the accretion disk at a distance $R\gtrsim 10^{10}$\,cm from the neutron star. At a distance $R\sim 10^{11}$\,cm, where the total surface density in the disk reaches ${\Sigma }_0\sim 20$\,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 $T_{atm}\sim (2÷3)\times 10^6$\,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 $\gtrsim 10$\,% accuracy in the range of X-ray photon energies $E<20$\,keV.

19 pages, 8 figures, published in Astronomy Letters

References in corpus (1)

• Modeling of non-stationary accretion disks in X-ray novae A 0620-00 and GRS 1124-68 during outburst

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