NuSTAR J095551+6940.8: a highly magnetized neutron star with super-Eddington mass accretion
NuSTAR J095551+6940.8: a highly magnetized neutron star with super-Eddington mass accretion
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DOI：
10.1093/mnras/stv170
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发表时间：
2014-12
影响因子：
4.8
通讯作者：
S. Dall’Osso;R. Perna;L. Stella
中科院分区：
文献类型：
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作者：
S. Dall’Osso;R. Perna;L. Stella
M82 中的超光 X 射线源 (ULX) X-2 被鉴定为吸积脉冲星，这为了解 ULX 子集的性质提供了新的线索，同时对超爱丁顿吸积的性质提出了新的问题。在这里，通过在磁螺纹盘场景的框架内对吸积脉冲星的扭矩方程进行数值求解，我们表明，对应于不同磁场值的三类解在数学上是允许的。我们认为，基于物理考虑和观察到的源特性，最高磁场（对应于 B $\sim 10^{13}$ G）受到青睐。特别是，这是唯一可以解释 $\dot{P}$ 中观察到的变化（超过四个时间间隔）的解决方案，而不需要 $\dot{M}$ 发生重大变化，这与同一时间内源的近似恒定的 X 射线发射不一致。对于这个解决方案，我们发现源只能容纳中等量的光束，0.5 $\lesssim b < 1$。最后，我们证明档案观测中的光度上限 L$_X < 2.5 \times 10^{38}$ erg s$^{-1}$ 与当时处于螺旋桨阶段的高磁化中子星一致。
The identification of the Ultraluminous X-ray source (ULX) X-2 in M82 as an accreting pulsar has shed new light on the nature of a subset of ULXs, while rising new questions on the nature of the super-Eddington accretion. Here, by numerically solving the torque equation of the accreting pulsar within the framework of the magnetically threaded-disk scenario, we show that three classes of solutions, corresponding to different values of the magnetic field, are mathematically allowed. We argue that the highest magnetic field one, corresponding to B $\sim 10^{13}$ G, is favoured based on physical considerations and the observed properties of the source. In particular, that is the only solution which can account for the observed variations in $\dot{P}$ (over four time intervals) without requiring major changes in $\dot{M}$, which would be at odds with the approximately constant X-ray emission of the source during the same time. For this solution, we find that the source can only accomodate a moderate amount of beaming, 0.5 $\lesssim b < 1$. Last, we show that the upper limit on the luminosity, L$_X < 2.5 \times 10^{38}$ erg s$^{-1}$ from archival observations, is consistent with a highly-magnetized neutron star being in the propeller phase at that time.