K-fluorescence lines in spectra of X-ray binaries

The reflection of the X-rays in K lines of heavy elements from a cold surface is calculated. The radiative transfer is treated rigorously, with the albedo in K lines expressed in terms of the H-function for isotropic scattering. This approach is also applied to evaluate the spectral shape of the low-energy wing of the line formed by the singly scattered K photons. A detailed discussion is given of the main characteristics of K-emission from the X-ray binaries. The prospects of observations of the narrow K-alpha lines in X-ray binaries are analyzed, with special attention paid to the information that can be obtained from such observations. The minimum equivalent width which one could expect in the case of the iron K-alpha line is evaluated for a number of well-known X-ray binaries.