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Is there a link between the neutron-star spin and the frequency of the kilohertz quasi-periodic oscillations?


  • Mariano Méndez,

    Corresponding author
    1. Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, the Netherlands
    2. Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, the Netherlands
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  • Tomaso Belloni

    1. INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (LC), Italy
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There is a general consensus that the frequencies of the kilohertz quasi-periodic oscillations (kHz QPOs) in neutron-star low-mass X-ray binaries are directly linked to the spin of the neutron star. The root of this idea is the apparent clustering of the ratio of the frequency difference of the kHz QPOs, and the neutron-star spin frequency, Δν/νs, at around 0.5 and 1 in 10 systems for which these two quantities have been measured. Here, we re-examine all available data of sources for which there exist measurements of two simultaneous kHz QPOs and spin frequencies, and we advance the possibility that Δν and νs are not related to each other. We discuss ways in which this possibility could be tested with current and future observations.