Quasiperiodic Phenomena in Accreting Binary Stars

Abstract

The discovery of quasiperiodic oscillations (QPOs) and low-frequency noise (LFN) in the light curves of low-mass x-ray binaries has led to the formation of a “unified model” which successfully, but not uniquely, accounts for the average Fourier power spectra of most x-ray binaries showing QPOs. It also makes specific predictions on the short time scale correlations and behavior of the QPOs and LFN. Because the flux from QPO sources is too low to detect individual QPO cycles, measurements of QPOs and LFN on short time scales have large uncertainties. Several statistical algorithms are employed in attempts to explore short time scale relationships between the power spectral components, and to characterize QPO attributes and moments of the intensity distribution. Narrow band frequency filter algorithms can be used to search for evidence of QPO amplitude variability and to search for evidence of short time scale correlations between QPO and LFN strengths and source intensity. The envelopes of QPO and LFN waveforms may be constrained from the moments of the light curves, especially the skewness. We briefly describe each of these tests, and others, warn about the systematic biases present, and show how tests of this type can constrain the standard model for QPOs.