Quasi-Periodic Oscillations in Low-Mass X-ray Binaries

Abstract

Strong, persistent, high-frequency QPO (quasi-periodic oscillations) have been discovered with EXOSAT in seven luminous, persistently bright low-mass X-ray binaries. The detailed properties of these QPO, in particular their dependence on source intensity, are discussed. A large variety is observed in the relations between source intensity and QPO frequency. If QPO frequency is simply related to accretion rate, as is the prediction of most proposed QPO models, then a matching large variety of relations between accretion rate and X-ray intensity will be required - a strong departure from the traditionally assumed strict proportionality.