标题： 关于Z源水平分支振荡的磁层拍频和Lense-Thirring解释 显示英文标题

标题： On the Magnetospheric Beat-Frequency and Lense-Thirring Interpretations of the Horizontal Branch Oscillation in the Z Sources

摘要： 我们研究了水平分支振荡（HBO）以及两个同时出现的千赫兹QPO，并将其性质与磁层拍频模型和Lense-Thirring进动模型的预测进行了比较。我们发现，由纯粹偶极子恒星磁场和辐射压力主导的内吸积盘所预测的磁层拍频模型中的HBO频率随吸积率的变化很好地符合观测到的变化趋势。该模型表明Z源中的中子星接近磁自旋平衡状态，其磁场强度约为10^9-10^10高斯，且这些源的临界快度参数大于0.8。如果千赫兹QPO的上支频率是吸积盘中的轨道频率，则磁层拍频模型需要吸积盘中的少量气体在3-4个恒星半径处不能与恒星磁场强烈耦合，而是以近似圆周运动缓慢向内漂移，直到靠近中子星表面几公里范围内。Lense-Thirring进动模型仅在Z源中子星的惯性矩为现实中子星状态方程所预测最大值的4-5倍时才与观测到的HBO频率一致。HBO与上支千赫兹QPO频率之间的相关性趋势并不符合该模型。我们认为当上支千赫兹QPO频率大于850Hz时，水平分支振荡频率与上支千赫兹QPO频率之间相关性的斜率变化直接与千赫兹QPO的频率分离变化有关。 显示英文摘要

摘要： We study the horizontal branch oscillations (HBO) and the two simultaneous kilohertz QPOs comparing their properties in five Z sources with the predictions of the magnetospheric beat-frequency and Lense-Thirring precession models. We find that the variation of the HBO frequency with accretion rate predicted by the magnetospheric beat-frequency model for a purely dipolar stellar magnetic field and a radiation-pressure-dominated inner accretion disk agrees well with the observed variation. This model implies that the neutron stars in the Z sources are near magnetic spin equilibrium, that their magnetic field strengths are ~10^9-10^10 G, and that the critical fastness parameter for these sources is >0.8. If the frequency of the upper kilohertz QPO is an orbital frequency in the accretion disk, the magnetospheric beat-frequency model requires that a small fraction of the gas in the disk does not couple strongly to the stellar magnetic field at 3-4 stellar radii but instead drifts slowly inward in nearly circular orbits until it is within a few kilometers of the neutron star surface. The Lense-Thirring precession model is consistent with the observed magnitudes of the HBO frequencies only if the moments of inertia of the neutron stars in the Z sources are 4-5 times larger than the largest values predicted by realistic neutron-star equations of state. The trend of the correlation between the HBO and upper kHz QPO frequencies is not consistent with this model. We argue that the change in the slope of the correlation between the frequency of the horizontal branch oscillation and the frequency of the upper kilohertz QPO, when the latter is greater than 850 Hz, is directly related to the varying frequency separation of the kilohertz QPOs.