The correlations between the spin frequencies and kHz QPOs of neutron stars in LMXBs

Free access article

Issue		A&A Volume 471, Number 2, August IV 2007


Page(s)		381 - 384
Section		Astrophysical processes
DOI		http://dx.doi.org/10.1051/0004-6361:20077069

A&A 471, 381-384 (2007)
DOI: 10.1051/0004-6361:20077069

The correlations between the spin frequencies and kHz QPOs of neutron stars in LMXBs

H. X. Yin¹, C. M. Zhang¹, Y. H. Zhao¹, Y. J. Lei², J. L. Qu², L. M. Song², and F. Zhang²

¹ 1. National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China
e-mail: zhangcm@bao.ac.cn
² 2. Astronomical Institute, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039, PR China

(Received 9 January 2007 / Accepted 7 May 2007)

Abstract
Aims.We studied the correlations between spin frequencies and kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries.
Methods.The updated data on kHz QPOs and spin frequencies are statistically analyzed.
Results. We find that when two simultaneous kHz QPOs are present in the power spectrum, the minimum frequency of upper kHz QPO is at least 1.3 times higher than the spin frequency, i.e. $\nu_{\rm s}<\nu_{\rm 2\,min}/1.3$ . We also find that the average kHz QPO peak separation in 6 Atoll sources anti-correlates with the spin frequency in the form $\langle \Delta\nu \rangle=-(0.19\pm0.05)\nu_{\rm s}+(389.40\pm21.67)$ Hz. If we shift this correlation in the direction of the peak separation by a factor of 1.5, this correlation matches the data points of the two accretion-powered millisecond X-ray pulsars, SAX J1808.4-3658 and XTE J1807-294.

Key words: X-rays: binaries -- accretion, accretion disks -- stars: neutron

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