Parkes observations for project P456 semester 2021APRS_10

The Parkes Pulsar Timing Array (PPTA) project has three primary goals: (a) detection of gravitational waves from astronomical sources, (b) establishment of a pulsar timescale, and (c) improvement of our understanding of Solar-system dynamics. The PPTA is the oldest of three international pulsar timing groups. We have the smallest telescope and the smallest group, but the best measurements and the best results. Our bound on the strength of the incoherent gravitational wave background is the only bound which significantly constrains theoretical models. We have maintained our leading position because: we have the southern sky; we have a small but well-focussed group; we have the best-calibrated receivers; and we have been able to observe with an almost regular cadence of 15 to 20 days over a wide bandwidth. With this proposal we aim to maintain our pre-eminent position in the field. Unlike most observing proposals, this is a continuing proposal for which the observations will continue to improve bounds on ultra-low-frequency gravitational waves until they are finally detected. Continued Parkes observations will remain valuable at least until the first stage of the SKA is able to improve on our sensitivity and observing cadence. Even after the gravitational wave background is detected we will want to continue observations in support of the nascent field of gravitational wave astronomy!

帕克斯脉冲星计时阵列（Parkes Pulsar Timing Array, PPTA）项目有三大核心目标：(a) 探测来自天文源的引力波；(b) 建立脉冲星时标系统；(c) 深化对太阳系动力学的认知。帕克斯脉冲星计时阵列是三大国际脉冲星计时研究组中历史最悠久的团队。我们虽拥有最小口径的望远镜与规模最精简的研究团队，却取得了最优的测量精度与研究成果。我们针对非相干引力波背景强度给出的观测约束，是目前唯一能显著约束相关理论模型的定量限制。我们始终保持领军地位的原因在于：坐拥南天球得天独厚的观测视野；团队规模小巧但目标高度聚焦；配备了校准最为完善的接收系统；并且能够以15至20天的近乎规则观测周期，在宽带宽范围内开展持续观测。本提案旨在维持我们在该领域的领军地位。与绝大多数观测提案不同，本提案属于持续性研究项目，相关观测将持续优化对超低频引力波的约束强度，直至最终实现直接探测。帕克斯望远镜的持续观测至少仍将具备科学价值，直至平方公里阵列（Square Kilometre Array, SKA）第一阶段项目能够实现优于我们的观测灵敏度与观测节奏。即便在引力波背景被成功探测之后，我们仍将持续开展观测，以支持这一新兴的引力波天文学研究领域！