Parkes observations for project P456 semester 2018OCTS_07

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 at three different wavelengths. With this proposal we aim to maintain our pre-eminent position in the field.\r\n\r\nUnlike 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!

Parkes脉冲星计时阵列（Parkes Pulsar Timing Array, PPTA）项目设有三大核心目标：(a) 探测来自各类天文源的引力波；(b) 建立标准化脉冲星时标；(c) 深化对太阳系动力学机制的认知。PPTA是三大国际脉冲星计时研究团队中历史最为悠久的一支。尽管我们拥有规模最小的望远镜与科研团队，却产出了当前最优质的观测数据与研究成果。我们针对非相干引力波背景强度给出的约束条件，是目前唯一能够显著限制相关理论模型的观测约束。我们能够始终保持领域领先地位的原因在于：拥有得天独厚的南天天区观测视野；团队规模小巧但目标高度聚焦；配备了校准精度最优的射电接收机；且能够以15至20天的近乎固定观测周期，在三个不同射电波段开展持续观测。通过本提案，我们旨在巩固并维持在该领域的领先地位。

与绝大多数观测提案不同，本提案属于持续性观测项目，相关观测工作将持续优化超低频引力波的约束精度，直至最终实现这类引力波的直接探测。至少在平方千米阵（Square Kilometre Array, SKA）第一阶段项目能够突破我们当前的探测灵敏度与观测周期之前，帕克斯望远镜的持续观测仍将具备极高的科学价值。即便引力波背景被成功探测，我们仍需延续观测工作，以支撑新兴的引力波天文学领域的发展。