Normal-branch quasi-periodic oscillations during the high-intensity state of Cygnus X-2

被引:11
作者
Wijnands, R
van der Klis, M
机构
[1] MIT, Ctr Space Res, Cambridge, MA 02139 USA
[2] Univ Amsterdam, Astron Inst Anton Pannekoek, NL-1098 SJ Amsterdam, Netherlands
关键词
accretion; accretion discs; stars : individual : Cygnus X-2; stars : neutron; X-rays : binaries; X-rays : individual : Cygnus X-2; X-rays : stars;
D O I
10.1046/j.1365-8711.2001.04058.x
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Using data obtained with the Rossi X-ray Timing Explorer, we report the detection of a 5-Hz quasi-periodic oscillation (QPO) in the bright low-mass X-ray binary and Z source Cygnus X-2 during high overall intensities (the high-intensity state). This QPO was detected on the so-called normal-branch and can be identified with the normal-branch QPO or NBO. Our detection of the NBO is the first one during times when Cygnus X-2 was in the high-intensity state. The rms amplitude of this QPO decreased from 2.8 per cent between 2 and 3.1 keV to <1.9 per cent between 5.0 and 6.5 keV. Above 6.5 keV, its amplitude rapidly increased to similar to 12 per cent rms above 16 keV. The time lags of the QPO were consistent with being zero below 5 keV (compared with the 2-3.1 keV band), but they rapidly increased to similar to 70 ms (140 degrees) around 10 keV, above which the time lags remained approximately constant near 70 ms. The photon energy dependences of the rms amplitude and the time lags are very similar to those observed for the NBO with other satellites (Ginga, EXOSAT) at different (i.e. lower) intensity states.
引用
收藏
页码:537 / 543
页数:7
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