Discovery of KiloHertz Quasi-Periodic Oscillations in the Z source GX 5-1

Abstract

We discovered two simultaneous kHz quasi-periodic oscillations (QPOs) in the bright low-mass X-ray binary and Z source GX 5-1 with the Rossi X-ray Timing Explorer. In the X-ray color-color and hardness-intensity diagram a clear Z track is traced out, which shifted between observations. The frequencies of the two kHz QPOs increased from ~215 Hz and ~500 Hz on the left part of the horizontal branch to ~700 Hz and ~890 Hz, respectively, on the upper part of the normal branch. With increasing frequency the FWHM and rms amplitude (8.6-60 keV) of the higher-frequency kHz QPO decreased from 300 to 30 Hz, and from 6.6 to 2.4%, respectively. The FWHM and amplitude of the lower-frequency kHz QPO (50-100 Hz and 3-4% rms) did not correlate with the position of the source on the Z track. The kHz QPO separation was consistent with being constant at 298+/-11 Hz. Simultaneously with the kHz QPOs horizontal branch oscillations (HBOs) were detected with frequencies between 18 and 56 Hz.

11 Pages, 4 figures (one color figure). Accepted for publication in the Astrophysical Journal Letters

References in corpus (6)

• Lense-Thirring Precession and QPOs in Low Mass X-Ray Binaries
• Kilohertz QPO Peak Separation Is Not Constant in Scorpius X-1
• KiloHertz Quasi-Periodic Oscillations in GX 17+2
• Discovery of KiloHertz Quasi-Periodic Oscillations in the Z source Cygnus X-2
• The Beat-Frequency Interpretation of Kilohertz QPOs in Neutron Star Low-Mass X-ray Binaries
• Discovery of kilohertz quasi-periodic oscillations in the Z source GX 340+0

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