Neutron stars provide a powerful probe of axion dark matter, especially in higher frequency ranges where there remain fewer laboratory constraints. Populations of neutron stars near the Galactic Centre have been proposed as a means to place strong constraints on axion dark matter. One downside of this approach is that there are very few direct observations of neutron stars in this region, introducing uncertainties in the total number of neutron stars in this “invisible” population at the Galactic Centre, whose size must be inferred through birth rate modelling. We suggest this number could also be reduced due to stellar dynamics carrying stars away from the Galactic Centre via large kick velocities at birth. We attempt to circumvent the uncertainty on the Galactic Centre population size by modelling the axion signal from better understood populations outside the Galactic Centre using PsrPopPy which is normalised against pulsar observations. We consider lower-frequency, wider-angle searches for this signal via a range of instruments including MeerKAT and SKA-low but find that the sensitivity is not competitive with existing constraints. Finally, returning to the Galactic Centre, we compare populations to single objects as targets for axion detection. Using the latest modelling of axion-photon conversion in the Galactic Centre magnetar, we conclude that within astrophysical uncertainties, the Galactic Centre population and the magnetar could give comparable sensitivities to axion dark matter, suggesting one should continue to search for both signals in future surveys.

中文翻译：

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来自中子星群的轴子信号


中子星为轴子暗物质提供了强大的探针，尤其是在实验室限制较少的较高频率范围内。银河系中心附近的中子星种群已被提议作为对轴子暗物质施加强烈限制的一种手段。这种方法的一个缺点是，在这个区域对中子星的直接观测非常少，这给银河系中心这个“看不见的”种群中的中子星总数带来了不确定性，其大小必须通过出生率建模来推断。我们认为这个数字也可以减少，因为恒星动力学在出生时通过大踢速度将恒星带离银河中心。我们试图通过使用 PsrPopPy 对来自银河中心之外更易理解的种群的轴子信号进行建模来规避银河中心种群规模的不确定性，该种群根据脉冲星观测进行了归一化。我们考虑通过包括 MeerKAT 和 SKA-low 在内的一系列仪器对该信号进行低频、更广角的搜索，但发现灵敏度与现有约束相比没有竞争力。最后，回到银河系中心，我们将种群与作为轴子检测目标的单个物体进行比较。使用银河系中心磁星中轴子-光子转换的最新模型，我们得出结论，在天体物理学的不确定性范围内，银河系中心种群和磁星可能对轴子暗物质具有相当的敏感性，这表明人们应该在未来的调查中继续寻找这两个信号。