Parkes observations for project P456 semester 2018APRS_07

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!

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。我们虽拥有规模最小的望远镜与研究团队，却取得了精度最高的测量结果与最优的科研产出。我们针对非相干引力波背景强度给出的约束条件，是目前唯一能显著约束相关理论模型的关键约束。我们能够始终保持领域领先地位的原因在于：我们拥有南天穹的独特观测区位；拥有一支精干且目标聚焦的研究团队；配备了校准精度最优的接收系统；并且能够以15至20天的近乎恒定观测周期，在三个不同观测波段开展持续观测。通过本项目申请，我们旨在维持本领域的卓越领先地位。

与绝大多数观测申请不同，本申请属于持续性观测项目，相关观测将持续优化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。Parkes望远镜的持续观测至少将保有重要科研价值，直至平方千米阵（Square Kilometre Array, SKA）第一阶段项目能够在观测灵敏度与周期上实现对我们的超越。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！