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Discovery of twin kHz quasi-periodic oscillations in the high galactic la titude X-ray transient XTE J2123--058

Jeroen Homan·Mariano Mendez·Rudy Wijnands·Michiel van der Klis·Jan van Paradijs
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Abstract

We report the discovery of twin kHz quasi-periodic oscillations (QPOs) in the persistent X-ray flux of the new X-ray transient XTE J2123-058. We detected the QPOs in data taken with the proportional counter array on board the Rossi X-ray Timing Explorer on 1998 July 14, when the source count rate was at about 50% of its outburst peak level. The frequencies of the QPOs were 853+/-4 Hz and 1129+/-8 Hz. The peaks had widths of 32 (+11/-8) Hz and 50 (+17/-13) Hz and the rms amplitudes were 6.1% (+0.7/-0.6) and 6.5% (+0.9/-0.8), respectively. The QPO frequencies increased marginally with count rate and the amplitudes showed a small increase with photon energy. On the basis of the appearance in the color-color and hardness-intensity diagrams, the low-frequency power spectrum, and the strength of the kHz QPOs, the system can be classified as an atoll source. The source showed five type I X-ray bursts. The distance to the source is estimated to be about 10 (5-15) kpc, which combined with the high Galactic latitude of 36.2 degrees indicates the source is a located in the Galactic halo.

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Jeroen Homan, Mariano Mendez, Rudy Wijnands, Michiel van der Klis, Jan van Paradijs. 1999-01-13. Discovery of twin kHz quasi-periodic oscillations in the high galactic la titude X-ray transient XTE J2123--058. https://doi.org/10.1086/311919

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