Einstein observations of high luminosity X-ray binaries

Recent observational advances in the study of high luminosity x-ray binaries have permitted investigation of the interaction of the outgoing x-radiation with the accreting matter surrounding the compact object. In two sources, 4U1822-37 and 4U2129+47, extended EINSTEIN coverage has led to the detection of partial x-ray eclipses, which indicate that the x-ray emitting regions must be extended in size. These have been interpreted as evidence for a large Compton-thick corona produced by evaporation of cool material off the surface of an accretion disk. In three other sources, 4U1915-05, 4U1624-49, and Cygnus X-2, evidence has been found for short x-ray absorption dips which are likely to be associated with obscuration by cool dense matter at the outer edge of the disk. In 4U1915-05, these dips are strictly periodic and determine the binary period for the system. In Cygnus X-2, the dips appear to be quasiperiodic, while in 4U1624-49, insufficient coverage has prevented clarification of the temporal properties of the absorption.For the brightest cosmic x-ray source, Scorpius X-1, the EINSTEIN objective grating spectrometer has provided high resolution spectra (λ/Δλ ～50) in the wavelength range 40-10 Å. The spectra reveal absorption features due to intervening helium, nitrogen, and oxygen. The implied nitrogen and oxygen abundances are anomalous and suggest that the absorbing material is intrinsic accreting matter which has been transferred from the surface of an evolved companion. Constraints on the inclination of the system then imply that this cool dense material must be well out of the orbital plane of the binary.