Parkes observations for project P1317 semester 2024APRS_01

The existence of a population of millisecond pulsars (MSPs) in the Galactic bulge is supported, among others, by the Fermi GeV excess, a signal of gamma rays coming from the Galactic center (GC) direction and resembling the cumulative emission of known MSPs. A previous study showed that, while these MSPs are unresolved in gamma rays, some of them could have been detected in past X-ray observations. The authors also identified a large number of MSP candidates among unidentified X-ray sources. By analyzing unpublished radio images, we found interesting radio counterparts to 6 of those candidates, and were granted 20h of observations with the Green Bank Telescope to settle on their nature. We discovered a new MSPs, PSR J1740-2807, towards one of our X-ray targets, bringing to 3 the number of highly-dispersed MSPs in the GC direction and probably unveiling the first direct evidence of a bulge MSP population. We propose to carry out regular timing of this pulsar with Parkes, in order to reveal its properties and potentially claim association with the original X-ray source. The follow up of this source will have a major impact on our understanding of the Fermi GeV excess, but will also benefit the main questions of modern physics like the nature of dark matter, possibly annihilating into gamma rays in the Galactic center, and the equation of state of cold dense matter, which can be constrained from X-ray observations of MSPs.

银河系核球（Galactic bulge）中存在毫秒脉冲星（millisecond pulsars, MSPs）群的结论，得到了包括费米GeV超出（Fermi GeV excess）在内的多项观测证据支持：费米GeV超出是指源自银心（Galactic center, GC）方向的伽马射线信号，其光谱特征与已知毫秒脉冲星的累积辐射高度相似。此前一项研究表明，尽管这类毫秒脉冲星在伽马射线波段无法被分辨，但其中部分天体已在过往X射线观测中被探测到；该研究团队还从未经证认的X射线源中甄别出大量毫秒脉冲星候选体。我们通过分析未公开发表的射电图像，为其中6个候选体找到了具有研究价值的射电对应体，并获批使用绿岸望远镜（Green Bank Telescope）开展20小时的观测以确定其物理本质。我们在针对其中一个X射线观测目标的观测中发现了一颗新的毫秒脉冲星PSR J1740-2807，使得银心方向高度弥散的毫秒脉冲星数量增至3颗，这很可能首次直接证实了银核球内存在毫秒脉冲星群。我们提议利用帕克斯望远镜（Parkes）对该脉冲星开展常规计时观测，以揭示其物理属性，并确认其与原始X射线源的关联。对该天体的后续研究不仅将极大推动我们对费米GeV超出起源的认知，还将助力解决现代物理学中的若干核心问题：例如暗物质（dark matter）的本质——暗物质可能在银心区域发生湮灭并产生伽马射线，以及冷致密物质的物态方程，后者可通过毫秒脉冲星的X射线观测得到约束。