KHz QPOs in LMXBs, relations between different frequencies and compactness of stars

Abstract

We suggest that the mass of four compact stars SAX J1808.4$-$3658, KS 1731$-$260, SAX J1750.8$-$2900 and IGR J17191$-$2821 can be determined from the difference in the observed kiloHertz quasi periodic oscillations (kHz QPO-s) of these stars. The stellar radius is very close to the marginally stable orbit $R_{ms}$ as predicted by Einstein's general relativity. It may be noted that the first of these stars was suggested to be a strange star more than a decade back by Li \emph{et al.} (1999) from the unique millisecond X-ray pulsations with an accurate determination of its rotation period. It showed kHz QPO-s eight years back and so far it is the only set that has been observed. This is the first time we give an estimate of the mass of the star and of three other compact stars in Low-Mass X-ray Binaries using their observed kHz QPO-s.

Accepted for publication in New Astronomy

References in corpus (8)

• The distribution of kHz QPO frequencies in bright LMXBs
• Optical spectroscopy and photometry of SAX J1808.4-3658 in outburst
• On the kHz QPO frequency correlations in bright neutron star X-ray binaries
• Is there a link between the neutron-star spin and the frequency of the kilohertz quasi-periodic oscillations?
• A review of rapid X-ray variability in X-ray binaries
• The correlations between the spin frequencies and kHz QPOs of Neutron Stars in LMXBs
• Compact strange stars with a medium dependence in gluons at finite temperature
• Difficulties with the QPOs Resonance Model

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• An X-ray high-frequency quasi-periodic oscillation in NGC 1365
• Detection and Characterization of Quasi-Periodic Oscillations in Seyfert Galaxy NGC 4151