X-Ray Burster Spectra in the State of the Persistent Flux Level - Two-Temperature Models of the Neutron Star Atmosphere

The X ray emission from accretion disks in low mass X ray binaries is discussed. The effects of transfer radiation and comptonization are taken into account. It is assumed that the atmosphere of a neutron star consists of two layers. The upper one is much hotter than the lower one. The presence of accretion is required. Self-consistent calculations of the spectrum of outgoing radiation for a wide range of luminosities and temperatures of the hot upper layer are presented. The observations proved to be consistent with the models whose hot layer temperature is of the order of 4 keV and the luminosity level is relatively low.