Observation of Kilohertz Quasiperiodic Oscillations from the Atoll   Source 4U 1702-429
  We present results of Rossi X-Ray Timing Explorer (XTE) observations of the atoll source 4U 1702-429 in the middle of its luminosity range. Kilohertz-range quasiperiodic oscillations (QPOs) were observed first as a narrow (FWHM ~7 Hz) peak near 900 Hz, and later as a pair consisting of a narrow peak in the range 625--825 Hz and a faint broad (FWHM 91 Hz) peak. When the two peaks appeared simultaneously the separation was 333 +/- 5 Hz. Six type I thermonuclear bursts were detected, of which five exhibited almost coherent oscillations near 330 Hz, which makes 4U 1702-429 only the second source to show burst oscillations very close to the kilohertz QPO separation frequency. The energy spectrum and color-color diagram indicate that the source executed variations in the range between the ``island'' and ``lower banana'' atoll states. In addition to the kilohertz variability, oscillations at ~10, ~35, and 80 Hz were also detected at various times, superimposed on a red noise continuum. The centroid of the \~35 Hz QPO tracks the frequency of the kilohertz oscillation when they were both present. A Lense-Thirring gravitomagnetic precession interpretation appears more plausible in this case, compared to other atoll sources with low frequency QPOs. 
Craig B. Markwardt (1,2), Tod E. Strohmayer (1), Jean H. Swank (1)   ((1) NASA/Goddard Space Flight Center, (2) National Res...