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 language | English (US) |
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Pages (from-to) | L35-L38 |
Journal | Astrophysical Journal |
Volume | 504 |
Issue number | 1 PART II |
DOIs | |
State | Published - 1998 |
Externally published | Yes |
Keywords
- Accretion, accretion disks
- Stars: Individual (gx 5-1)
- Stars: Neutron
- X-rays: Stars
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science