Discovery of Two Simultaneous Kilohertz Quasi-periodic Oscillations in the Persistent Flux of GX 349+2

Abstract

We report the discovery of two simultaneous quasi-periodic oscillations in the persistent flux of GX 349+2 at frequencies 712±9 and 978±9 Hz, with rms amplitudes 1.25%±0.34% and 1.34%±0.32%, respectively. During our 152 ks observation with the Rossi X-ray Timing Explorer, GX 342+2 was in either the normal branch or the flaring branch with count rates in the nominal 2-60 keV RXTE-PCA band ranging from a low of 8000 counts s-1 to a high of 15,000 counts s-1. The kHz QPOs were observed only when the source was at the top of the normal branch, when the count rate was about 8200 counts s-1, corresponding to a flux of 1.4×10−8 ergs cm-1 s-1 in the 2-10 keV band. With this report, now kHz QPOs have been observed in all six Z sources.