Discovery of kilohertz quasi-periodic oscillations in the Z source GX 5-1

Citation
R. Wijnands et al., Discovery of kilohertz quasi-periodic oscillations in the Z source GX 5-1, ASTROPHYS J, 504(1), 1998, pp. L35-L38
Citations number
22
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Space Sciences
Journal title
ASTROPHYSICAL JOURNAL
ISSN journal
0004-637X → ACNP
Volume
504
Issue
1
Year of publication
1998
Part
2
Pages
L35 - L38
Database
ISI
SICI code
0004-637X(19980901)504:1<L35:DOKQOI>2.0.ZU;2-N
Abstract
We discovered two simultaneous kHz quasi-periodic oscillations (QPOs) in th e bright low-mass X-ray binary and Z source GX 5-1 with the Rossi X-ray Tim ing Explorer. In the X-ray color-color and hardness-intensity diagram a cle ar Z track is traced out, which shifted between observations. The frequenci es of the two kHz QPOs increased from similar to 215 and similar to 500 Hz on the left part of the horizontal branch to similar to 700 and similar to 890 Hz, respectively, on the upper part of the normal branch. With increasi ng frequency the FWHM and rms amplitude (8.6-60 keV) of the higher frequenc y 1kHz 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. Th e kHz QPO separation was consistent with being constant at 298 +/- 11 Hz. S imultaneously with the kHz QPOs horizontal branch oscillations were detecte d with frequencies between 18 and 56 Hz.