A Possible Explanation for the "Parallel Tracks" Phenomenon in Low-Mass X-Ray Binaries
A Possible Explanation for the "Parallel Tracks" Phenomenon in Low-Mass X-Ray Binaries
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DOI：
10.1086/323378
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发表时间：
2001-06
影响因子：
1.4
通讯作者：
M. Klis
中科院分区：
文献类型：
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作者：
M. Klis
对低质量 X 射线双星 (LMXB) 中的观测结果提出了一种解释，一方面大多数可观测的 X 射线光谱和计时参数与另一方面 X 射线光度之间的相关性，虽然在给定源的几小时时间尺度上通常良好，但在较长的时间尺度上和源之间都不存在。这种现象在 kHz 准周期振荡 (QPO) 源中尤其明显，导致此类参数与光度的关系图中出现平行轨迹。需要指出的是，先前提出的解释需要至少两个随时间变化的独立参数，例如通过盘的吸积率和通过径向流入的吸积率，实际上只要一个自变量就足够了，只要对该变量的时间变化的系统响应具有即时分量和时间平均分量。探索了一个特定的场景，其中大多数可观测的一阶光谱和时间参数取决于由其自身长期平均值标准化的盘吸积率，而不是任何单独的吸积率（相反，光度仅取决于总吸积率）。这提供了一种方法，其中参数可以与吸积率不相关，但响应于吸积率的变化而变化。对这种模型进行了数值模拟，描述了 kHz QPO 频率与 X 射线光度之间的关系，其观测特征是频率与光度平面中的平行轨迹的显着图案，无论是在单个源中还是跨源。事实证明，该模型非常好地再现了观察结果。建议采用物理解释来产生这种情况；特别有希望的解释似乎涉及径向流入，其速率是通过盘吸积速率的时间平均过程得出的，而内盘半径则取决于盘吸积与总光度之间的平衡。讨论了这个想法对我们理解 LMXB 中的状态和轨迹的影响，并简要讨论了该想法对观测情况更为复杂的黑洞候选者的适用性。
An explanation is proposed for the observation that in low-mass X-ray binaries (LMXBs), the correlation between most observable X-ray spectral and timing parameters on the one hand, and X-ray luminosity on the other, while generally good in a given source on a timescale of hours, is absent both on longer timescales and between sources. This phenomenon, particularly evident in kHz quasi-periodic oscillation (QPO) sources, leads to parallel tracks in plots of such parameters versus luminosity. It is pointed out that where previously proposed explanations require at least two time-variable independent parameters, such as accretion rate through the disk and through a more radial inflow, just one independent variable is in fact sufficient, provided that the systemic response to time variations in this variable has both a prompt and a time-averaged component. A specific scenario is explored in which most observable spectral and timing parameters to first order depend on the disk accretion rate normalized by its own long-term average, rather than on any individual accretion rate (luminosity, on the contrary, just depends on the total accretion rate). This provides a way in which parameters can be uncorrelated with accretion rate, yet vary in response to variations in accretion rate. Numerical simulations are presented of such a model, describing the relation between kHz QPO frequency and X-ray luminosity, which observationally is characterized by a striking pattern of parallel tracks in the frequency versus luminosity plane, both in individual sources and across sources. The model turns out to reproduce the observations remarkably well. Physical interpretations are suggested that would produce such a scenario; particularly promising seems an interpretation involving a radial inflow with a rate that derives through a time-averaging process from the disk accretion rate, and an inner disk radius that depends on the balance between the accretion through the disk and the total luminosity. The consequences of this idea for our understanding of states and tracks in LMXBs are discussed, and the applicability of the idea to black hole candidates, where the observational situation is more complex, is briefly addressed.