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arXiv 1602.08841astro-ph.HE
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通过模拟中子星系统kHz量子点的能量相关时滞来约束康普顿化介质的尺寸

Constraining the size of the Comptonizing medium by modeling the energy dependent time-lags of kHz QPOs of Neutron star system

Nagendra Kumar, Ranjeev Misra

摘要:

在早期的工作中,我们已经表明,所观察到的软滞后和r.m.s与能量的低kHz QPO的中子星双星可以解释的框架下的热康普顿化模型。它还表明,这样的解释可以提供的康普顿介质的大小和几何形状的估计。在这里,我们研究的依赖性,这些估计的时间平均谱模型假设和QPO的频率。利用1996年3月3日RXTE对4U 1608-52的高质量时间滞后和均方根值,以及其它在不同QPO频率下的观测结果,其中两个宽能带之间存在单一时间滞后。我们比较了当假设时间平均光谱由光谱退化的“热”和“冷”种子光子光谱模型表示时所得到的结果。我们发现,对于“热”种子光子模型,介质的尺寸在0.3-2.0公里的范围内,随着QPO频率的增加,尺寸减小。另一方面,对于“冷”种子光子模型,尺寸的范围大得多,为0.5-20 km,因此可能不显示出随QPO频率的变化。我们的研究结果强调需要宽带光谱信息结合高频定时,以解除这种简并。我们进一步表明,作为能量的函数的上kHz QPO的均方根值是类似的较低的一个,我们确实发现,该QPO的驱动程序应该是相同的较低kHz QPO的日冕的温度变化。然而,对于上kHz QPO报告的时间滞后是困难的,如果证实,将挑战这里提出的简单康普顿化模型。这可能意味着混响滞后也很重要,和/或主导频谱分量不是单一温度介质,而是多温度复杂介质。

英文摘要:

In earlier works, we had shown that the observed soft lags and r.m.s versus energy of the lower kHz QPO of neutron star binaries can be explained in the framework of a thermal Comptonization model. It was also shown that such an interpretation can provide estimates of the size and geometry of the Comptonizing medium. Here we study the dependence of these estimates on the time-averaged spectral model assumed and on the frequency of the QPO. We use the high quality time lag and r.m.s obtained during March 3rd 1996 observation of 4U 1608-52 by RXTE as well as other observations of the source at different QPO frequencies where a single time-lag between two broad energy bands have been reported. We compare the results obtained when assuming that the time-averaged spectra are represented by the spectrally degenerate "hot" and "cold" seed photon spectral models. We find that for the "hot" seed photon model the medium size is in the range of 0.3-2.0 kms and the size decreases with increasing QPO frequency. On the other hand for the "cold" seed photon model the range for the sizes are much larger 0.5-20 kms and hence perhaps show no variation with QPO frequency. Our results emphasis the need for broad band spectral information combined with high frequency timing to lift this degeneracy. We further show that the r.m.s as a function of energy for the upper kHz QPO is similar to the lower one and indeed we find that the driver for this QPO should be temperature variations of the corona identical to the lower kHz QPO. However, the time lag reported for the upper kHz QPO is hard, which if confirmed, would challenge the simple Comptonization model presented here. It would perhaps imply that reverberation lags are also important and/or the dominate spectral component is not a single temperature medium but a multi-temperature complex one.

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