Observation of Kilohertz Quasiperiodic Oscillations from the Atoll Source 4U 1702−429 by RXTE

We present results of Rossi X-Ray Timing Explorer (RXTE) observations of the atoll source 4U 1702−429 in the middle of its luminosity range. Kilohertzrange 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. Subject headings: accretion, accretion disks — stars: individual (4U 1702−429) — stars: neutron