Wijnands R, Van Der Klis M, Homan J, Chakrabarty D, Markwardt C B, Morgan E H
School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, UK.
Nature. 2003 Jul 3;424(6944):44-7. doi: 10.1038/nature01754.
The relativistic plasma flows onto neutron stars that are accreting material from stellar companions can be used to probe strong-field gravity as well as the physical conditions in the supra-nuclear-density interiors of neutron stars. Plasma inhomogeneities orbiting a few kilometres above the stars are observable as X-ray brightness fluctuations on the millisecond dynamical timescale of the flows. Two frequencies in the kilohertz range dominate these fluctuations: the twin kilohertz quasi-periodic oscillations (kHz QPOs). Competing models for the origins of these oscillations (based on orbital motions) all predict that they should be related to the stellar spin frequency, but tests have been difficult because the spins were not unambiguously known. Here we report the detection of kHz QPOs from a pulsar whose spin frequency is known. Our measurements establish a clear link between kHz QPOs and stellar spin, but one not predicted by any current model. A new approach to understanding kHz QPOs is now required. We suggest that a resonance between the spin and general relativistic orbital and epicyclic frequencies could provide the observed relation between QPOs and spin.
相对论性等离子体流向正在从恒星伴星吸积物质的中子星，这可用于探测强场引力以及中子星超核密度内部的物理条件。在恒星上方几公里处轨道运行的等离子体不均匀性，可作为流的毫秒动力学时间尺度上的X射线亮度波动被观测到。千赫兹范围内的两个频率主导着这些波动：双千赫兹准周期振荡（kHz QPOs）。这些振荡起源的竞争模型（基于轨道运动）都预测它们应该与恒星自旋频率有关，但由于自旋并不明确可知，测试一直很困难。在此，我们报告了从一个自旋频率已知的脉冲星中检测到kHz QPOs。我们的测量在kHz QPOs和恒星自旋之间建立了明确的联系，但这是目前任何模型都未预测到的。现在需要一种理解kHz QPOs的新方法。我们认为，自旋与广义相对论轨道频率和周转频率之间的共振可以提供观测到的QPOs与自旋之间的关系。
