Parkes observations for project P456 semester 2020APRS_01

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.\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!

帕克斯脉冲星计时阵列（Parkes Pulsar Timing Array，PPTA）项目设有三大核心目标：（a）探测来自天文天体的引力波，（b）建立脉冲星时标系统，（c）深化对太阳系动力学的认知。PPTA是三大国际脉冲星计时合作组中历史最悠久的一个。我们拥有的望远镜与团队规模均为三者中最小，但观测精度与研究成果却最为出色。我们针对非相干引力波背景强度给出的约束，是目前唯一能有效限制相关理论模型的观测约束。我们能始终保持领先地位的原因在于：坐拥南半球天空的观测优势、拥有规模小巧却目标明确的团队、配备经过最优校准的接收系统，以及能够以15至20天的近乎固定周期在宽带宽下开展持续观测。本提案旨在维持我们在该领域的领先地位。

与多数观测提案不同，本提案属于持续性项目，相关观测将持续优化极低频引力波的观测约束，直至最终直接探测到该信号。帕克斯望远镜的持续观测至少仍将保有科学价值，直到平方公里阵列（Square Kilometre Array，SKA）第一阶段项目能够在灵敏度与观测周期上超越我们。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！