低频QPO谱和Lense-Thirring进动
Low frequency QPO spectra and Lense-Thirring precession
摘要：
我们证明了黑洞双星（和中子星）功率密度谱中的低频QPO可以用Lense-Thirring进动来解释。这在过去已经被提出过很多次，简单的单半径模型可以通过减小特征半径来定性地匹配所观察到的QPO频率的增加，正如截断圆盘模型所预测的那样。然而，这也预示了频率强烈地依赖于自旋，并且在最后稳定轨道处给出了最大频率，该最大频率通常远高于在所有黑洞双星中观察到的~ 10 Hz的显著恒定的最大频率。我们的模型的关键方面，使它符合这些意见是，进动是一个径向延伸的区域的热内流。外半径由圆盘的截断半径设定，如上所述，但内半径位于最后稳定轨道之外，数值模拟表明，对于未对准的流动，密度急剧下降。物理上对该内半径的解析估计表明，它随a_* 增加，以几乎完全抵消随自旋增加的预期频率的方式降低预期频率。如所观察到的，这将最大预测频率束缚在10 Hz左右，而与a_* 无关。这是第一个QPO模型，它解释了频率和频谱的背景下，一个完善的几何吸积流。
英文摘要：
We show that the low frequency QPO seen in the power density spectra of black hole binaries (and neutron stars) can be explained by Lense-Thirring precession. This has been proposed many times in the past, and simple, single radius models can qualitatively match the observed increase in QPO frequency by decreasing a characteristic radius, as predicted by the truncated disc models. However, this also predicts that the frequency is strongly dependent on spin, and gives a maximum frequency at the last stable orbit which is generally much higher than the remarkably constant maximum frequency at ~10Hz observed in all black hole binaries. The key aspect of our model which makes it match these observations is that the precession is of a radially extended region of the hot inner flow. The outer radius is set by the truncation radius of the disc as above, but the inner radius lies well outside of the last stable orbit at the point where numerical simulations show that the density drops off sharply for a misaligned flow. Physically motivated analytic estimates for this inner radius show that it increases with a_*, decreasing the expected frequency in a way which almost completely cancels the expected increase with spin. This ties the maximum predicted frequency to around 10Hz irrespective of a_*, as observed. This is the first QPO model which explains both frequencies and spectrum in the context of a well established geometry for the accretion flow.
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