1999ApJ...513L.119H

We report the discovery of twin kilohertz 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 and 1129±8 Hz. The peaks had widths of 32⁺¹¹_–8 and 50⁺¹⁸_–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 indicates that the source is a located in the Galactic halo.