具有多极磁场的吸积高磁化中子星的超爱丁顿辐射
Super-Eddington Emission from Accreting, Highly Magnetised Neutron Stars with a Multipolar Magnetic Field
摘要：
脉冲超亮X射线源（PULX）的特征在于极大的光度（$ > 10^{40} \text{erg s}^{-1}$）。虽然有一个普遍的共识，它们拥有一个吸积，磁化中子星（NS），如何产生光度$> 100$乘以爱丁顿极限，$L_E$，太阳质量的物体的问题仍然存在争议。一个有希望的解释依赖于在强磁场存在下不透明度的减少，这使得局部通量比爱丁顿通量大得多。然而，避免螺旋桨效应的发生可能是一个严重的问题。在这里，我们重新考虑柱吸积到一个高度磁化NS的问题，通过放松假设一个纯偶极场，并允许更复杂的磁场拓扑结构，延长以前发表的计算。我们发现最大亮度主要由NS表面附近的磁场强度决定。我们还研究了决定吸积柱几何形状和出射光度的其他因素，例如对控制盘-磁层边界吸积流的参数的假设。我们的结论是，一个强磁化NS与$\sim 10^{13} \text{G}$的偶极分量，$\sim10^{14} \text{G}$的八极分量和自旋周期$\sim1 \text{s}$可以产生亮度的$\sim 10^{41} \text{erg s}^{-1}$，而避免螺旋桨制度。我们将我们的模型应用到两个脉冲星，NGC 5907 ULX-1和NGC 7793 P13，并讨论如何解释它们的光度和自旋周期率在不同的配置，无论是有或没有多极磁性组件。
英文摘要：
Pulsating ultra-luminous X-ray sources (PULXs) are characterised by an extremely large luminosity ($ > 10^{40} \text{erg s}^{-1}$). While there is a general consensus that they host an accreting, magnetized neutron star (NS), the problem of how to produce luminosities $> 100$ times the Eddington limit, $L_E$, of a solar mass object is still debated. A promising explanation relies on the reduction of the opacities in the presence of a strong magnetic field, which allows for the local flux to be much larger than the Eddington flux. However, avoiding the onset of the propeller effect may be a serious problem. Here, we reconsider the problem of column accretion onto a highly magnetized NS, extending previously published calculations by relaxing the assumption of a pure dipolar field and allowing for more complex magnetic field topologies. We find that the maximum luminosity is determined primarily by the magnetic field strength near the NS surface. We also investigate other factors determining the accretion column geometry and the emergent luminosity, such as the assumptions on the parameters governing the accretion flow at the disk-magnetosphere boundary. We conclude that a strongly magnetized NS with a dipole component of $\sim 10^{13} \text{G}$, octupole component of $\sim10^{14} \text{G}$ and spin period $\sim1 \text{s}$ can produce a luminosity of $\sim 10^{41} \text{erg s}^{-1}$ while avoiding the propeller regime. We apply our model to two PULXs, NGC 5907 ULX-1 and NGC 7793 P13, and discuss how their luminosity and spin period rate can be explained in terms of different configurations, either with or without multipolar magnetic components.
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