两种X射线源亚群的运动学差异
Kinematic distinction of the two subpopulations of X-ray pulsars
摘要：
Be/X射线双星的总体分布显示出双峰性的强有力证据，特别是在中子星的自旋周期中。几种物理机制可能产生这种双峰性。Be/X射线双星中两个不同的超新星通道或不同的中子星吸积模式是最有希望的候选机制。研究这些系统的运动学可能会对这种双峰的物理特性提供一些额外的见解。如果这两个Be/X射线双星子群来自两种不同的超新星类型，那么这两个子群应该有不同的特殊（系统）速度。这可以通过测量系统的速度来直接测试，或者通过测量系统相对于其发源地的位置来间接测试。利用最新的Gaia数据集和最新的小麦哲伦星云（SMC）星表，分析了Be/X射线双星在银河系中的切向奇异速度和Be/X射线双星在SMC中的位置。我们使用系统到最近的年轻星团的距离作为系统切向速度的代表。我们应用统计检验来研究由中子星自旋划分的两个子群是否在运动学上也是不同的。有证据表明，这两个亚群在运动学上确实不同。然而，这两个子群的切向特有速度与不同超新星通道假说的预期相反。我们发现了一些边缘证据（$p \approx$~0.005），表明来自短自旋亚群的银河Be/X射线双星比来自长自旋亚群的系统具有系统性更高的特有速度。同样的效果，但较弱的，也恢复了SMC Be/X射线双星的所有考虑的集群目录。
英文摘要：
The population of Be/X-ray binaries shows strong evidence of bimodality, especially in the spin period of neutron stars. Several physical mechanisms may produce this bimodality. The most favored candidate mechanisms are two distinct supernova channels or different accretion modes of the neutron stars in Be/X-ray binaries. Investigating the kinematics of these systems may provide some additional insight into the physics of this bimodality. If the two Be/X-ray binary subpopulations arise from two distinct supernova types, then the two subpopulations should have different peculiar (systemic) velocities. This can be tested either directly, by measuring the velocity of the system, or indirectly, by measuring the position of the system with respect to its birthplace. Using the most recent Gaia dataset and the newest catalogs of Small Magellanic Cloud (SMC) star clusters, we analyzed the tangential peculiar velocities of Be/X-ray binaries in the Galaxy and the positions of Be/X-ray binaries in the SMC. We used the distance of the system from the nearest young star cluster as a proxy to the tangential velocity of the system. We applied statistical testing to investigate whether the two subpopulations that are divided by the spin of the neutron star are also kinematically distinct. There is evidence that the two subpopulations are indeed kinematically distinct. However, the tangential peculiar velocities of the two subpopulations are the reverse from what is expected from the distinct supernova channel hypothesis. We find some marginal evidence ($p \approx$~0.005) that the Galactic Be/X-ray binaries from the short-spin subpopulation have systematically higher peculiar velocities than the systems from the long-spin subpopulation. The same effect, but weaker, is also recovered for the SMC Be/X-ray binaries for all considered cluster catalogs.
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