论文标题
在X射线脉冲星GX 301-2的旋转事件和旋转方向上
On the spin-up events and spin direction of the X-ray pulsar GX 301-2
论文作者
论文摘要
最近，提出了一个逆行中子恒星，用于经典的风馈X射线脉冲星GX 301-2，以解释基于在Periastron附近旋转逆转的轨道旋转，该旋转基于以前解释GX 301-2的periastron flare的流模型。我们详细研究了Fermi/GBM检测到的三个罕见的自旋事件，并发现自旋衍生物与Swift/Bat Fluxes相关，并在$ \dotν\ propto f^{0.75 \ pm0.05} $之后。 GX 301-2的所有旋转事件始于Periastron后10天，这是潮汐剥离的气体到达中子恒星所需的时间。光学伴侣的缓慢旋转表明，积聚的物质可能在轨道运动方向上具有角动量，就像在类似Roche-Lobe的溢出中一样。结果，GX 301-2的旋转事件将有利于在序列中子恒星中积聚前期磁盘。我们还发现，GX 301-2的固有X射线发射的耀斑发生在Periastron前0.4天，而低能量发射（2-10 KEV）的耀斑发生在Periastron前1.4天。先前的低能耀斑可以通过更强的固有X射线发射更接近Periastron来解释。这一发现削弱了流模型的需求。 Periastron附近的GX 301-2的脉冲分数严重减少，这可能是由康普顿散射过程引起的。来自光学伴侣的康普顿反射可能是GX 301-2的观察到的轨道自旋逆转。
Recently a retrograde neutron star is proposed for the classical wind-fed X-ray pulsar, GX 301-2, to explain the orbital spin-up to spin-down reversal near periastron, based on the stream model invoked to explain the pre-periastron flare of GX 301-2 previously. We study in detail three rare spin-up events detected by Fermi/GBM and find that the spin derivatives are correlated with the Swift/BAT fluxes, following a relation of $\dotν\propto F^{0.75\pm0.05}$. All the spin-up events of GX 301-2 started about 10 days after the periastron, which is the time needed for tidally stripped gas to reach the neutron star. The slow rotation of the optical companion implies that the accreted matter is likely to have angular momentum in the direction of the orbital motion, as in a Roche-Lobe-like overflow. As a result, the spin-up events of GX 301-2 would favor accretion of a prograde disk to a prograde neutron star. We also find that the flare of intrinsic X-ray emission of GX 301-2 happened 0.4 days before periastron, while the flare of low energy emission (2-10 keV) happened about 1.4 days before periastron. The preceding low energy flare can be explained by stronger absorption of the intrinsic X-ray emission closer to the periastron. This finding weakened the need of the stream model. The pulse fraction of GX 301-2 near periastron is reduced heavily, which is likely caused by Compton scattering process. Compton reflection from the optical companion might be responsible for the observed orbital spin reversal of GX 301-2.
