Parkes observations for project P456 semester 2018APRS_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 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!

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。尽管我们的望远镜与团队规模均为三者中最小，但却获得了最精准的测量数据与最优异的研究成果。我们针对非相干引力波背景（incoherent gravitational wave background）强度给出的约束，是目前唯一能显著约束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：拥有南天区观测视野；拥有一支规模小巧但目标高度聚焦的团队；配备了校准精度最优的接收系统；并且能够以15至20天的近乎恒定观测间隔，在三个不同波段开展观测。通过本提案，我们旨在维持本领域的领军地位。

与多数观测提案不同，本提案属于持续性观测项目，相关观测将持续优化极低频引力波（ultra-low-frequency gravitational waves）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在平方千米阵列（Square Kilometre Array，SKA）第一阶段能够提升我们的灵敏度与观测间隔之前，都将保有其科学价值。即便非相干引力波背景（incoherent gravitational wave background）被成功探测，我们仍将继续开展观测，以支撑新兴的引力波天文学（gravitational wave astronomy）领域发展！