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 By analyzing unpublished radio images, we found interesting radio counterparts to 6 of those candidates, and were granted 20h of observations with the Green Bank Telescope to settle on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.

银河核球中存在毫秒脉冲星（millisecond pulsars, MSPs）群体这一推论，得到了费米GeV过剩（Fermi GeV excess）的支持：该信号源自银心（Galactic center, GC）方向的伽马射线，其辐射特征与已知毫秒脉冲星的累积伽马射线发射高度相似。此前一项研究表明，尽管这些毫秒脉冲星在伽马射线波段尚未被分辨，但其中部分个体已在过往的X射线观测中被探测到。该研究团队还在未证认的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的射电图像，为其中6个候选体找到了极具研究价值的射电对应体，并获准使用绿岸望远镜（Green Bank Telescope）开展20小时的观测以确定其物理本质。我们在其中一个X射线观测目标方向发现了一颗新的毫秒脉冲星PSR J1740-2807，使银心方向高度弥散的毫秒脉冲星数量增至3颗，这一发现很可能首次直接证实了银河核球中存在毫秒脉冲星群体。我们提议使用帕克斯望远镜（Parkes）对该脉冲星开展常规计时观测，以明确其物理属性，并有望证实其与原始X射线源的关联。对该源的后续研究不仅将极大推动我们对费米GeV过剩的认知，还将助力解决现代物理学中的若干核心问题——例如可能在银心发生湮灭并产生伽马射线的暗物质本质，以及可通过毫秒脉冲星的X射线观测加以约束的冷密物质物态方程。