Highly coherent kilohertz quasi-periodic oscillations from a neutron star X-ray binary EXO 1745-248

Abstract

We report the discovery ($20\sigma$) of kilohertz quasi-periodic oscillations (kHz QPOs) at ~ 690 Hz from the transient neutron star low-mass X-ray binary EXO 1745-248. We find that this is a lower kHz QPO, and systematically study the time variation of its properties using smaller data segments with and without the shift-and-add technique. The quality (Q) factor occasionally significantly varies within short ranges of frequency and time. A high Q-factor (264.5 +- 38.5) of the QPO is found for a 200 s time segment, which might be the largest value reported in the literature. We argue that an effective way to rule out kHz QPO models is to observationally find such high Q-factors, even for a short duration, as many models cannot explain a high coherence. However, as we demonstrate, the shift-and-add technique cannot find a very high Q-factor which appears for a short period of time. This shows that the coherences of kHz QPOs can be higher than the already high values reported using this technique, implying further constraints on models. We also discuss the energy dependence of fractional rms amplitude and Q-factor of the kHz QPO.

Minor changes, typos corrected, reference added; 8 pages, 5 figures, accepted for publication in The Astrophysical Journal Letters

References in corpus (4)

• Faint X-ray Sources in the Globular Cluster Terzan 5
• The coherence of kHz quasi-periodic oscillations in the X-rays from accreting neutron stars
• On the maximum amplitude and coherence of the kilohertz quasi-periodic oscillations in low-mass X-ray binaries
• The drop of the coherence of the lower kHz QPOs is also observed in XTE J1701-462

Cited by in corpus (5)

• A Systematic Spectral-Timing Analysis of Kilohertz Quasi-Periodic Oscillations in the Rossi X-ray Timing Explorer Archive
• Superburst with Outburst from EXO 1745-248 in Terzan 5 with MAXI
• High-frequency variability in neutron-star low-mass X-ray binaries
• Period doubling and non-linear resonance in the black hole candidate IGR J17091-3624 ?
• An XMM-Newton and INTEGRAL view on the hard state of EXO 1745-248 during its 2015 outburst