Parkes observations for project P456 semester 2019APRS_30

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.

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）项目共有三大核心目标：（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支。尽管我们所使用的望远镜与团队规模均为三者中最小，却取得了最精准的测量数据与最优异的科研成果。我们针对非相干引力波背景强度给出的约束，是目前唯一能对相关理论模型形成有效限制的约束条件。我们能始终保持领域领先地位的原因在于：我们坐拥得天独厚的南天球观测天区；拥有一支规模精干且目标高度聚焦的团队；配备了经过最优校准的接收系统；并且能够以15至20天为间隔的近乎规律的观测节奏，在宽频带范围内开展观测。通过本提案，我们旨在维持本领域的领先地位。

与绝大多数观测提案不同，本提案属于持续性观测项目，相关观测将持续收紧极低频引力波的约束边界，直至最终实现这类引力波的直接探测。至少在平方千米阵（Square Kilometre Array, SKA）一期工程能够实现比我们更高的探测灵敏度与更优的观测节奏之前，帕克斯望远镜的持续观测仍将具备重要科研价值。即便引力波背景被成功探测，我们仍需持续开展观测，以支撑这一新兴的引力波天文学领域的发展！