Parkes observations for project P456 semester 2018OCTS_47

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.

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）项目拥有三大核心科学目标：（a）探测来自天体源的引力波；（b）建立标准化脉冲星时标系统；（c）深化对太阳系动力学机制的认知。PPTA是全球三大国际脉冲星计时研究组中历史最悠久的团队。尽管我们拥有的望远镜与研究团队规模均为三者中最小，但却斩获了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，是目前唯一能够显著约束相关理论模型的观测限制。我们能够始终保持领域领先地位的原因在于：我们拥有南天半球的专属观测视野；拥有一支规模虽小但高度聚焦的专业团队；配备了经过最优校准的射电接收系统；并且能够以15至20天的近乎规律的观测周期，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研究领域的领军地位。

与绝大多数观测提案不同，本提案属于持续性观测项目，其观测工作将持续提升对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）第一阶段完成部署并实现优于我们的观测灵敏度与周期之前，帕克斯天文台的持续观测仍将具备极高的科学价值。即便在引力波背景被成功探测之后，我们仍将继续开展观测，以支撑这一新兴的引力波天文学领域的发展。