Correlations in Quasi‐periodic Oscillation and Noise Frequencies among Neutron Star and Black Hole X‐Ray Binaries

We study systematically the ~0.1-1200 Hz quasi-periodic oscillations (QPOs)and broad noise components observed in the power spectra of non-pulsingneutron-star and black-hole low-mass X-ray binaries. We show that among thesecomponents we can identify two, occurring over a wide range of source types andluminosities, whose frequencies follow a tight correlation. The variabilitycomponents involved in this correlation include neutron-star kilohertz QPOs andhorizontal-branch oscillations, as well as black-hole QPOs and noisecomponents. Our results suggest that the same types of variability may occur inboth neutron-star and black-hole systems over three orders of magnitude infrequency and with coherences that vary widely but systematically. Confirmationof this hypothesis will strongly constrain theoretical models of thesephenomena and provide additional clues to understanding their nature.