Parkes observations for project P456 semester 2019APRS_25

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）项目具备三大核心科学目标：（a）探测来自天体源的引力波；（b）建立脉冲星时标系统；（c）深化对太阳系动力学机制的认知。PPTA是全球三大国际脉冲星计时研究团队中历史最为悠久的一支。尽管我们的望远镜与团队规模均为三者中最小，但却取得了最优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，是目前唯一能显著限制相关理论模型的约束结果。我们能够始终保持领域领先地位的原因在于：具备南半球天空的观测区位优势；拥有一支规模虽小但目标高度聚焦的研究团队；配备了校准精度最优的接收机；并且能够以近乎恒定的15至20天观测周期，在宽带宽范围内开展观测。本提案旨在维持我们在该领域的领先地位。 与绝大多数观测提案不同，本提案属于持续性研究项目，其观测工作将持续优化对超低频引力波的约束精度，直至最终成功探测到这类引力波。至少在平方千米阵列（Square Kilometre Array, SKA）的第一阶段项目能够在灵敏度与观测周期上超越我们之前，帕克斯望远镜的持续观测仍将具备极高科研价值。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，以支撑新兴的引力波天文学领域发展！