Discovery of Kilohertz Quasi-periodic Oscillations in the Z Source GX 5-1

Rudy Wijnands, Mariano Méndez, Michiel van der Klis, Dimitrios Psaltis, Erik Kuulkers, Frederick K. Lamb

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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 and ~500 Hz on the left part of the horizontal branch to ~700 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 were detected with frequencies between 18 and 56 Hz.
Original languageEnglish
Pages (from-to)L35-L38
JournalThe Astrophysical Journal
Volume504
Issue number1
DOIs
Publication statusPublished - 1-Sep-1998
Externally publishedYes

Keywords

  • ACCRETION
  • ACCRETION DISKS
  • STARS: INDIVIDUAL ALPHANUMERIC: GX 5-1
  • STARS: NEUTRON
  • X-RAYS: STARS
  • Accretion
  • Accretion Disks
  • Stars: Individual: Alphanumeric: GX 5-1
  • Stars: Neutron
  • X-Rays: Stars

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