Kilohertz Quasi-periodic Oscillation Peak Separation Is Not Constant in the Atoll Source 4U 1608–52
Kilohertz Quasi-periodic Oscillation Peak Separation Is Not Constant in the Atoll Source 4U 1608–52
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DOI：
10.1086/311600
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发表时间：
1998-07
期刊：
影响因子：
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通讯作者：
Mariano Méndez;M. Klis;R. Wijnands;Eric C. Ford;J. Paradijs;B. Vaughan
中科院分区：
文献类型：
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作者：
Mariano Méndez;M. Klis;R. Wijnands;Eric C. Ford;J. Paradijs;B. Vaughan
我们提出了新的罗西X射线定时探测器观测的低质量X射线双星4U 1608-52在其1998年爆发的衰变。我们检测到，通过直接快速傅立叶变换方法，第二千赫准周期振荡（kHz QPO）的存在，在其功率密度谱，这是以前只看到通过灵敏度增强的“移位和添加”技术。这个结果证实4U 1608-52是一个双kHz QPO源。当较低kHz QPO的频率从470 Hz增加到865 Hz时，这两个QPO之间的频率间隔显著降低，从325.5±3.4 Hz降低到225.3±12.0 Hz，这与简单的拍频解释相矛盾。kHz QPO的峰值分离的这种变化与先前在天蝎座X-1中看到的非常相似，但发生在平均亮度低10倍的地方。我们讨论了这一结果的框架内，已提出的kHz QPO模型。拍频模型的峰值分离与中子星星的自旋速率，以及先前提出的解释类似的行为在天蝎座X-1，强烈挑战这一结果。
We present new Rossi X-Ray Timing Explorer observations of the low-mass X-ray binary 4U 1608-52 during the decay of its 1998 outburst. We detect, by a direct fast Fourier transform method, the existence of a second kilohertz quasi-periodic oscillation (kHz QPO) in its power density spectrum, which was previously only seen by means of the sensitivity-enhancing "shift and add" technique. This result confirms that 4U 1608-52 is a twin kHz QPO source. The frequency separation between these two QPOs decreased significantly, from 325.5±3.4 to 225.3±12.0 Hz, as the frequency of the lower kHz QPO increased from 470 to 865 Hz, in contradiction with a simple beat-frequency interpretation. This change in the peak separation of the kHz QPOs is closely similar to that previously seen in Scorpius X-1 but takes place at a 10 times lower average luminosity. We discuss this result within the framework of models that have been proposed for kHz QPO. Beat-frequency models where the peak separation is identified with the neutron star spin rate, as well as the explanations previously proposed to account for the similar behavior of the QPOs in Sco X-1, are strongly challenged by this result.