THE SURVEY OF LOW-MASS X-RAY BINARIES WITH THE EINSTEIN-OBSERVATORY SOLID-STATE SPECTROMETER AND MONITOR PROPORTIONAL COUNTER

The HEAO 2 or Einstein solid-state spectrometer (SSS; 0.5-4.5 keV) and monitor proportional counter (MPC; 1.2-20.0 keV) carried out an exten sive survey of 49 low-mass X-ray binaries (LMXBs). Simultaneous SSS pl us MPC spectra, selected on the basis of their intensity, were fitted with a set of simple and complex spectral models. For all the sources, including Eddington-limited bulge sources, bursters, dippers, the sof t spectrum black hole candidates, and a few transients in decline, the spectra could be fitted acceptably with combinations of thermal brems strahlung and blackbody models or a Comptonized spectrum and a blackbo dy. The results rule out optically thick disk models for the bright (Z ) sources and power-law models for the bursters. The SSS can confirm o nly the strongest of previously reported low-energy emission lines due to O VIII or Fe L transitions. Uncertainties in column densities are modest, and together with consideration of a disk distribution of gas and dust in the galaxy, the column densities provide distance estimate s. These are the only measures yet available for eight sources. Severa l physical interpretations in terms of an optically thick component lo cated on or very near the neutron star, an optically thin region farth er in radius from the neutron star, and contribution of the accretion disk are possible. Assumptions required of the pulsar in a cocoon mode l are problematical. Correlations of spectral parameters with intensit y observed in color-color diagrams are more complex than previously re ported, although relating luminosity changes to the mass accretion rat e is still tenable.