Study on the Energy Limits of kHz QPOs in Sco X-1 with RXTE and Insight-HXMT Observations
Study on the Energy Limits of kHz QPOs in Sco X-1 with RXTE and Insight-HXMT Observations
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DOI：
10.3847/1538-4357/abf6d5
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发表时间：
2021-04
期刊：
影响因子：
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通讯作者：
S. Jia;J. Qu;F. Lu;S. Zhang;S. Zhang;Y. Huang;D. Wang;D. Zhou;G. Xiao;Q. Bu;
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文献类型：
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作者：
S. Jia;J. Qu;F. Lu;S. Zhang;S. Zhang;Y. Huang;D. Wang;D. Zhou;G. Xiao;Q. Bu;
我们利用罗西x射线定时探测器（RXTE）和硬x射线调制望远镜（Insight-HXMT）的数据，对Sco X-1中的千赫兹准周期振荡（kHz QPOs）进行了详细的频谱定时分析。首次研究了可检测到kHz QPOs的能带：在水平分支上，RXTE检测到的上、下kHz QPOs分别为~ 6.89-24.01和~ 8.68-21.78 keV， Insight-HXMT检测到的上kHz QPOs为~ 9-27.5 keV；下法向分支的能带较窄。在较低的能量下，kHz QPOs的分数均方根（rms）随能量的增加而增加，在16和20 keV左右达到峰值，然后趋于平稳，尽管存在很大的不确定性。RXTE/PCA的死区效应仿真表明，死区对kHz qpo的搜索影响不大，但会使有效值幅度被低估。RXTE数据显示，在~ 6 keV以下没有检测到明显的QPO，这意味着kHz QPO不是来自吸积盘和中子星表面的黑体发射。此外，结合能量谱和绝对均势谱分析，我们认为Sco X-1中的kHz QPOs源于过渡层内部的Comptonization，其中旋转设置了频率，而向内的大块运动使频谱变得更加困难。
We present a detailed spectral-timing analysis of the Kilohertz quasiperiodic oscillations (kHz QPOs) in Sco X-1 using the data of the Rossi X-ray Timing Explorer (RXTE) and the Hard X-ray Modulation Telescope (Insight-HXMT). The energy band with detectable kHz QPOs is studied for the first time: on the horizontal branch, it is ∼6.89–24.01 and ∼8.68–21.78 keV for the upper and lower kHz QPOs, respectively, detected by the RXTE, and ∼9–27.5 keV for the upper kHz QPOs by the Insight-HXMT; on the lower normal branch, the energy band is narrower. The fractional root mean square (rms) of the kHz QPOs increases with energy at a lower energy, reaches a plateau at about 16 and 20 keV for the lower and upper peaks, and then levels off though with a large uncertainty. The simulation of the deadtime effect of RXTE/PCA shows that the deadtime does not affect much the search of the kHz QPOs but makes the rms amplitude underestimated. No significant QPO is detected below ∼6 keV as shown by the RXTE data, implying that the kHz QPOs do not originate from the blackbody emission of the accretion disk and neutron star surface. In addition, with the combined analysis of the energy spectra and the absolute rms spectra of kHz QPOs, we suggest that the kHz QPOs in Sco X-1 originate from the Comptonization of the inner part of the transition layer, where the rotation sets the frequency and the inward bulk motion makes the spectrum harder.