Hercules X-1 中 X 射线毫赫兹准周期振荡的观测
Observations of the X-ray Millihertz Quasiperiodic Oscillations in Hercules X-1
AI总结：
本研究通过Insight-HXMT观测数据，确认Her X-1中存在约0.01赫兹的X射线毫赫兹准周期振荡，并首次发现与共存的约0.005-0.009赫兹QPO，揭示两种QPO具有不同物理机制，分别与拍频和磁盘进动相关。
摘要：
基于2017年至2019年间大量Insight-HXMT观测数据，我们对持续X射线双星脉冲星Her X-1进行了系统的计时研究，确认了频率约为0.01赫兹的X射线毫赫兹准周期振荡（mHz QPOs）的存在。在数据分析过程中应用小波分析，我们首次识别出与约0.01赫兹QPO共存的约0.005-0.009赫兹QPO。小波分析表明，这些QPO特征表现出瞬态行为，mHz QPO的频率在短时间内演化。QPO质心频率（约0.005-0.009赫兹）与X射线光度之间存在正相关关系，而10毫赫兹QPO频率在不同光度下几乎保持不变，这表明两种类型的mHz QPO具有不同的物理机制。X射线和紫外波段的10毫赫兹QPO可能具有相同的起源，与Alfvén半径接近共转半径时的拍频有关，而5毫赫兹QPO可能起源于磁盘进动。
英文摘要：
With a systematic timing investigation of the persistent X-ray binary pulsar Her X-1 based on a large number of Insight-HXMT observations between 2017 to 2019, we confirm the presence of X-ray millihertz quasi-periodic oscillations (mHz QPOs) at $\sim 0.01$ Hz. By applying wavelet analysis in our data analysis procedures, we firstly identified $\sim 0.005-0.009$ Hz QPOs coexisting with the $\sim 0.01$ Hz QPOs. Wavelet analysis suggests that these QPO features show transient behaviors, frequencies of mHz QPOs evolved in short time scales. There exists a positive relation between QPO centroid frequency (from $\sim 0.005-0.009$ Hz) and the X-ray luminosity, while the 10 mHz QPO frequencies keep nearly constant for different luminosities, which suggests different physical mechanisms for two types of mHz QPOs. The 10 mHz QPOs in both X-ray and UV bands would have the same origin related to the beat frequency where the Alfv$\acute{e}$n radius is close to the corotation radius, and the 5 mHz QPOs may originate from magnetic disk precession.
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