来自Terzan 5的毫赫兹准周期振荡和热核爆发：燃烧状态的展示
Millihertz quasi-periodic oscillations and thermonuclear bursts from Terzan 5: A showcase of burning regimes
摘要：
我们提出了一个全面的研究热核爆发和毫赫兹准周期振荡（mHz QPO）的中子星（NS）的瞬态和11赫兹X射线脉冲星IGR J17480-2446，位于球状星团泰山5。我们在2010年爆发期间发现的爆发率增加，持续光度从爱丁顿极限的0.1倍上升到0.5倍，与热核燃烧理论定性一致，但与以前所有热核爆发的观测相反。随着吸积速率的增加，热核爆发逐渐演化为mHz的QPO，反之亦然。来自IGR J17480-2446的mHz QPO类似于先前在其他吸积NS中观察到的QPO，但它们具有较低的频率（约3倍），并且在持续光度较高时发生（4-25倍）。我们发现四个不同的突发制度和陡峭的（接近逆立方）减少的突发复发时间增加持续光度。我们将这些研究结果与核燃烧模型进行比较，并找到纯氦和混合氢/氦点火制度之间的过渡的证据时，持续的光度约为0.3倍的爱丁顿限制。我们还指出了重要的观测到的突发和理论之间的差异，预测更明亮，更频繁的突发，并建议在NS信封的额外的热源是必需的，以调和观测到的和预期的突发属性。我们讨论了NS磁场和自旋对预期的核燃烧制度的影响，在这个特定的脉冲星的背景下。
英文摘要：
We present a comprehensive study of the thermonuclear bursts and millihertz quasi-periodic oscillations (mHz QPOs) from the neutron star (NS) transient and 11 Hz X-ray pulsar IGR J17480-2446, located in the globular cluster Terzan 5. The increase in burst rate that we found during its 2010 outburst, when persistent luminosity rose from 0.1 to 0.5 times the Eddington limit, is in qualitative agreement with thermonuclear burning theory yet opposite to all previous observations of thermonuclear bursts. Thermonuclear bursts gradually evolved into a mHz QPO when the accretion rate increased, and vice versa. The mHz QPOs from IGR J17480-2446 resemble those previously observed in other accreting NSs, yet they feature lower frequencies (by a factor ~3) and occur when the persistent luminosity is higher (by a factor 4-25). We find four distinct bursting regimes and a steep (close to inverse cubic) decrease of the burst recurrence time with increasing persistent luminosity. We compare these findings to nuclear burning models and find evidence for a transition between the pure helium and mixed hydrogen/helium ignition regimes when the persistent luminosity was about 0.3 times the Eddington limit. We also point out important discrepancies between the observed bursts and theory, which predicts brighter and less frequent bursts, and suggest that an additional source of heat in the NS envelope is required to reconcile the observed and expected burst properties. We discuss the impact of NS magnetic field and spin on the expected nuclear burning regimes, in the context of this particular pulsar.
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