Kilohertz quasi-periodic oscillations as probes of the X-ray color-color diagram and neutron star accretion-disk structure for Z sources
Kilohertz quasi-periodic oscillations as probes of the X-ray color-color diagram and neutron star accretion-disk structure for Z sources
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千赫兹准周期振荡作为 X 射线彩色图和 Z 源中子星吸积盘结构的探针
DOI：
10.1051/0004-6361/202037435
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发表时间：
2020
影响因子：
6.5
通讯作者：
Jia Shu-Mei
中科院分区：
文献类型：
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作者：
Wang De-Hua;Zhang Cheng-Min;Qu Jin-Lu;Jia Shu-Mei
基于在中子星星低质量X射线双星（NS-LMXB）中观测到的kHz准周期振荡（QPO），研究了Cyg X-2、GX 5-1、GX 17+2和Sco X-1等Z射线源的NS磁层盘结构沿着Z轨道的演化.我们发现，所有源的磁层-盘半径（以kHz准周期振荡表示）沿Z轨道从水平分支（HB）到正常分支（NB）呈现沿着单调减小的趋势，这意味着当吸积盘向NS表面移动时，其主要辐射成分可能发生显著变化.此外，发现HB/NB顶点对应的具体半径约为r 20 km，这意味着X射线辐射模式的潜在过境特征位置。 此外，我们还发现，在NS表面附近发生的NB的半径为r <$16 - 20 km，系统地小于半径为r <$20 - 29 km的HB。 为了解释CCD特性与Z源特殊的磁层-盘半径之间的关系，我们认为，对应于NB的磁力线被“冻结”到等离子体中，并随着NS磁层-盘半径的缩小而进一步向内移动，并在NS表面附近堆积。然后，它们在r = 16−20 km附近形成一个强磁场区，在那里，高磁能密度和高等离子体质量密度可能主导了NB的辐射过程。
Based on the detected kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries (NS-LMXBs), we investigate the evolution of the NS magnetosphere-disk structure along the Z track in the X-ray color-color diagram (CCD) for luminous Z sources, such as Cyg X-2, GX 5-1, GX 17+2, and Sco X-1. We find that the magnetosphere-disk radiusrinferred by kHz QPOs for all the sources shows a monotonically decreasing trend along the Z track from the horizontal branch (HB) to the normal branch (NB), implying that the dominated radiation components may dramatically change as the accretion disk moves toward the NS surface. In addition, the specific radius that corresponds to the HB/NB vertex is found to be aroundr∼ 20 km, implying a potential characteristic position of transiting for the X-ray radiation mode. Furthermore, we find that the NBs that occur near the NS surface have a radius ofr∼ 16−20 km, which is systematically smaller than those of HBs that have radii ofr∼ 20−29 km. To interpret the relation between the CCD properties and the special magnetosphere-disk radii of Z sources, we suggest that the magnetic field lines corresponding to NB are “frozen-in” to the plasma, and move further inward with the shrinking of the NS magnetosphere-disk radius and pile up near the NS surface. They then form a strong magnetic field region aroundr∼ 16−20 km, where the high magnetic energy density and high plasma mass density may dominate the radiation process in NB.