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quasi-periodic oscillations(QPOs) Short-lived, periodic flux changes, frequently observed in low-mass X-ray binaries. They were first detected in EXOSAT observations, with typical frequencies being 1–20 Hz, and coherence lasting for several tens of pulses; such pulses cause broad peaks in the X-ray power spectra of the sources. These QPOs are believed to arise in oscillations associated with the accretion of matter onto the compact star (white dwarf or neutron star) in these systems, and may prove to be a generic signature of such accretion. More recent observations, particularly with RXTE, have shown more rapid QPOs, at kHz frequencies, possibly associated with the neutron star spin frequency.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006