Parkes observations for project P456 semester 2019APRS_21

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成员。尽管我们拥有的望远镜与研究团队规模均为三者中最小，但却取得了精度最高的测量结果与最出色的科研成果。我们针对非相干引力波背景强度给出的约束，是目前唯一可有效限制相关理论模型的观测约束。

我们能始终保持该领域领军地位的原因在于：依托南天球的独特观测区位、拥有精干且聚焦明确的研究团队、配备经过最优校准的接收系统，且能够以15至20天的近乎规律的观测周期，在宽带宽条件下开展持续观测。通过本次申请，我们旨在维持该领域的领军地位。

与绝大多数观测申请不同，本次申请属于持续性观测项目，相关观测将持续优化对超低频引力波的约束精度，直至最终实现引力波的直接探测。帕克斯望远镜的持续观测至少仍将具备科学价值，直至平方千米阵（Square Kilometre Array, SKA）第一阶段建成并在观测灵敏度与观测频次上超越我们。即便引力波背景被成功探测，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。