Low- and high-frequency variability as a function of spectral properties in the bright X-ray binary GX 5-1

被引:63
作者
Jonker, PG
van der Klis, M
Homan, J
Méndez, M
Lewin, WHG
Wijnands, R
Zhang, W
机构
[1] Univ Amsterdam, Astron Inst Anton Pannekoek, NL-1098 SJ Amsterdam, Netherlands
[2] SRON, NL-3584 CA Utrecht, Netherlands
[3] MIT, Dept Phys, Cambridge, MA 02138 USA
[4] MIT, Ctr Space Res, Cambridge, MA 02139 USA
[5] NASA, Goddard Space Flight Ctr, High Energy Astrophys Lab, Greenbelt, MD 20771 USA
关键词
accretion; accretion discs; stars : individual : GX 5-1; stars : neutron; X-rays : stars;
D O I
10.1046/j.1365-8711.2002.05442.x
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We report on a detailed analysis of data obtained over nearly four years with the Rossi X-ray Timing Explorer of the Z source GX 5-1. From a spectral analysis using a hardness-intensity diagram it was found that the source traced out the typical Z-shaped pattern. The study of the power spectral properties showed that when the source moved on the horizontal branch towards the normal branch the fractional rms amplitudes and time-scales of all variability decreased, while their FWHMs increased. The frequency separation of the two kHz QPO peaks decreased from 344+/-12 to 232+/-13 Hz, while the frequency of the lower and upper kHz QPO increased from 172+/-10 to 608+/-6 Hz and from 516+/-10 to 840+/-12 Hz, respectively. At low frequencies, besides the horizontal branch oscillation (HBO) and its second harmonic, two additional broad Lorentzian components were needed to obtain acceptable fits. These broad Lorentzians have Q -values of similar to1-2 and frequencies 0.5 and 1.5 times the HBO frequency. When interpreted as being related to the HBO, they seem to favour disc models for the HBO over the magnetic beat-frequency model. The frequency of the normal branch oscillations changed slightly and non-monotonically, while on the normal branch between similar to6 Hz at both ends and 5.25+/-0.05 Hz near the middle of the branch. It evolved into a flat-topped noise component on the flaring branch. We compared the timing properties of the some of the Z sources. We also compare the timing properties and colour-colour diagrams (CDs) of GX 5-1 with those of the back hole candidate XTE J1550-564 and the atoll source 4U 1608-52. The CDs are strikingly similar when a colour scheme commonly employed in back hole studies is used. However, this may be a degeneracy as the CDs turn out to be more complicated when colours common in neutron star studies are employed. Apart from some remarkable similarities between the CD of XTE J1550-564 and that of 4U 1608-52, several differences can be seen between these CDs and that of GX 5-1. Conclusions on spectral states or properties based solely on the use of CDs using the 'black hole scheme' should be regarded with caution.
引用
收藏
页码:665 / 678
页数:14
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