Mass-angular-momentum relations implied by models of twin peak quasi-periodic oscillations

Abstract

Twin peak quasi-periodic oscillations (QPOs) appear in the X-ray power-density spectra of several accreting low-mass neutron star (NS) binaries. Observations of the peculiar Z-source Circinus X-1 display unusually low QPO frequencies. Using these observations, we have previously considered the relativistic precession (RP) twin peak QPO model to estimate the mass of central NS in Circinus X-1. We have shown that such an estimate results in a specific mass-angular-momentum (M-j) relation rather than a single preferred combination of M and j. Here we confront our previous results with another binary, the atoll source 4U 1636-53 that displays the twin peak QPOs at very high frequencies, and extend the consideration to various twin peak QPO models. In analogy to the RP model, we find that these imply their own specific M-j relations. We explore these relations for both sources and note differences in the chi-square behavior that represent a dichotomy between high- and low-frequency sources. Based on the RP model, we demonstrate that this dichotomy is related to a strong variability of the model predictive power across the frequency plane. This variability naturally comes from the radial dependence of characteristic frequencies of orbital motion. As a consequence, the restrictions on the models resulting from observations of low-frequency sources are weaker than those in the case of high-frequency sources. Finally we also discuss the need for a correction to the RP model and consider the removing of M-j degeneracies, based on the twin peak QPO-independent angular momentum estimates.

16 pages, 7 figures

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Cited by in corpus (11)

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• Constraining models of twin peak quasi-periodic oscillations with realistic neutron star equations of state
• Confronting models for the high-frequency QPOs with Lense-Thirring precession
• Simple analytic formula relating the mass and spin of accreting compact objects to their rapid X-ray variability
• Appearance of innermost stable circular orbits of accretion discs around rotating neutron stars
• On one-parametric formula relating the frequencies of twin-peak quasi-periodic oscillations
• Test of the string loop oscillation model using kHz quasiperiodic oscillations in a neutron star binary
• Evidences of an innermost stable bound orbit predicted by general relativity from the amplitude of the twin-peak quasi-periodic oscillations
• Oscillation properties of relativistic tori in the vicinity of a distorted deformed compact object