Kilohertz Quasi-periodic Oscillation Frequency Anticorrelated with Millihertz Quasi-periodic Oscillation Flux in 4U 1608–52
Kilohertz Quasi-periodic Oscillation Frequency Anticorrelated with Millihertz Quasi-periodic Oscillation Flux in 4U 1608–52
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DOI：
10.1086/339771
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发表时间：
2002-02
期刊：
影响因子：
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通讯作者：
Wenfei Yu;M. van der Klis
中科院分区：
文献类型：
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作者：
Wenfei Yu;M. van der Klis
我们分析了1996年3月3日获得的低质量X射线双星和环礁源4U 1608-52的Rossi X射线定时探测器数据，其中该源同时显示出在840 Hz附近的强单千赫准周期振荡（kHz QPO）和在能量低于5 keV时检测到的7.5 mHz QPO。我们发现kHz QPO的频率与mHz QPO的2-5 keV X射线计数率近似成正比。平均kHz QPO频率在mHz QPO循环期间变化约0.6Hz（0.07%），在该mHz QPO循环期间，平均2-5 keV计数率变化约60个计数s-1（4%）。这与在较长时间尺度上的相同数据中观察到的频率-计数率相关性相反，因此构成了与通量起源相关的频率-通量相关性中的符号反转的第一个例子。这样的符号反转的辐射盘截断模型的情况下，通量的变化起源于中子星星，但不是由于磁盘吸积率波动预测。结果支持核燃烧的mHz QPO的解释和解释的kHz QPO频率的吸积盘的内边缘的轨道频率的指示器。由于准周期核燃烧的通量施加在内盘上的辐射应力的变化导致内盘半径的变化，因此，观察到kHz QPO频率和X射线计数率之间的关系。我们发现X射线计数率相对于kHz QPO频率的时滞约为10 s，这可能是由于中子星星上的核燃烧前沿远离赤道区传播造成的。
We analyzed Rossi X-Ray Timing Explorer data of the low-mass X-ray binary and atoll source 4U 1608-52 obtained on 1996 March 3 in which the source simultaneously showed a strong single kilohertz quasi-periodic oscillation (kHz QPO) around 840 Hz and a 7.5 mHz QPO detected at energies below 5 keV. We find that the frequency of the kHz QPO is approximately anticorrelated with the 2-5 keV X-ray count rate associated with the mHz QPO. The average kHz QPO frequency varies by about 0.6 Hz (0.07%) during a mHz QPO cycle over which the average 2-5 keV count rate varies by about 60 counts s-1 (4%). This is the opposite of the frequency-count rate correlation observed in the same data on longer timescales and, hence, constitutes the first example of a sign reversal in the frequency-flux correlation related to the origin of the flux. Such a sign reversal is predicted by the radiative disk truncation model for the case where the flux variations originate on the neutron star but are not due to disk accretion rate fluctuations. The results support the nuclear burning interpretation of the mHz QPO and the interpretation of the kHz QPO frequency as an indicator of the orbital frequency at the inner edge of the accretion disk. The varying radiative stresses exerted on the inner disk by the flux due to the quasi-periodic nuclear burning lead to changes in the inner disk radius and, hence, to the observed anticorrelation between kHz QPO frequency and X-ray count rate. We found a time lag of about 10 s of the X-ray count rate relative to the kHz QPO frequency in terms of the anticorrelation between these two quantities, which could be caused by the propagation of the nuclear burning front on the neutron star away from the equatorial region.