Parallel Tracks as Quasi-steady States for the Magnetic Boundary Layers in Neutron-star Low-mass X-Ray Binaries
Parallel Tracks as Quasi-steady States for the Magnetic Boundary Layers in Neutron-star Low-mass X-Ray Binaries
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DOI：
10.3847/1538-4357/aa9071
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发表时间：
2017-10
期刊：
影响因子：
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通讯作者：
M. Erkut;Onur Çatmabacak
中科院分区：
文献类型：
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作者：
M. Erkut;Onur Çatmabacak
低质量x射线双星（lmxb）中的中子星通常被认为是弱磁化的物体，它们以圆盘的形式从低质量伴星那里吸积物质。尽管与年轻的中子星系统相比较弱，但lmxb中的中子星磁球可以在确定光谱和时间特性之间的相关性方面发挥重要作用。出现在千赫兹（kHz）准周期振荡（QPO）频率与x射线通量平面的平行轨迹可以作为研究中子星lmxb中磁层-盘相互作用的工具。对于动力学上重要的弱场，在中子星表面附近截断的最内层盘极有可能形成非开普勒磁边界层。这样的边界区域可能包含千赫范围内频率的振荡模式。我们使用kHz QPOs的边界区域模型生成平行音轨。我们还提出了我们的模型的直接应用，以再现观察到的平行轨道的个别来源，如4U 1608-52, 4U 1636-53，和Aql X-1。我们揭示了边界层的径向宽度如何在每个源的长期通量演化中变化以重新生成平行轨迹。对于不同的源，径向宽度的运行看起来相似，并且可以通过描述边界区域长期平均稳定行为的一般模型函数来拟合。然后平行轨迹对应于源在平均趋势周围可能占据的准稳定状态。
The neutron stars in low-mass X-ray binaries (LMXBs) are usually thought to be weakly magnetized objects accreting matter from their low-mass companions in the form of a disk. Albeit weak compared to those in young neutron-star systems, the neutron-star magnetospheres in LMXBs can play an important role in determining the correlations between spectral and temporal properties. Parallel tracks appearing in the kilohertz (kHz) quasi-periodic oscillation (QPO) frequency versus X-ray flux plane can be used as a tool to study the magnetosphere–disk interaction in neutron-star LMXBs. For dynamically important weak fields, the formation of a non-Keplerian magnetic boundary layer at the innermost disk truncated near the surface of the neutron star is highly likely. Such a boundary region may harbor oscillatory modes of frequencies in the kHz range. We generate parallel tracks using the boundary region model of kHz QPOs. We also present the direct application of our model to the reproduction of the observed parallel tracks of individual sources such as 4U 1608–52, 4U 1636–53, and Aql X-1. We reveal how the radial width of the boundary layer must vary in the long-term flux evolution of each source to regenerate the parallel tracks. The run of the radial width looks similar for different sources and can be fitted by a generic model function describing the average steady behavior of the boundary region over the long term. The parallel tracks then correspond to the possible quasi-steady states the source can occupy around the average trend.