A review of quasi-periodic oscillations in low-mass X-ray binaries

In this paper we present a review of the quasi-periodic oscillations (QPO) observed in the X-ray flux of low-mass X-ray binaries. In Section 1 a general background is given on galactic populations of accretion-driven X-ray sources. Section 2 contains a description of the methods that have been used to analyze these QPO. In Section 3 the QPO observations are described in some detail. Models for the QPO are considered in Section 4. In Section 5 the time lags observed between QPO at different photon energies, and their possible implications for X-ray spectral models, are discussed. Our conclusions are summarized in Section 6.