Parkes observations for project P456 semester 2018OCTS_34

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一支。尽管我们的望远镜与研究团队规模均为三者中最小，但却斩获了精度最高的观测数据与最具影响力的研究成果。我们所给出的非相干引力波背景强度约束，是目前唯一能够显著约束相关理论模型的定量结果。本项目始终保持领域领军地位的原因在于：我们坐拥南天球天区的独特观测优势；拥有一支精干且目标高度聚焦的研究团队；配备了校准精度最优的射电接收机；并且能够以每15至20天近乎恒定的观测节奏，在三个不同观测波段开展持续观测。通过本次项目申请，我们旨在巩固本领域的领先地位。

与绝大多数观测申请不同，本次申请属于持续性研究项目，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。Parkes望远镜的持续观测至少在平方千米阵列（Square Kilometre Array, SKA）第一阶段达成优于当前的灵敏度与观测节奏之前，仍将具备不可替代的科学价值。即便在引力波背景被成功探测之后，我们仍将持续开展观测，以支撑这一新兴引力波天文学领域的发展与完善。