Parkes observations for project P456 semester 2021APRS_12

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!

Parkes脉冲星计时阵列（Parkes Pulsar Timing Array, PPTA）项目拥有三大核心目标：(a) 探测来自各类天体源的引力波；(b) 建立脉冲星时标（pulsar timescale）系统；(c) 深化对太阳系动力学（Solar-system dynamics）的认知。PPTA是三大国际脉冲星计时研究组中历史最悠久的团队。尽管我们拥有的望远镜与研究团队规模均为三者中最小，却取得了最优的观测数据与研究成果。我们针对非相干引力波背景（incoherent gravitational wave background）强度给出的约束，是目前唯一能显著限制相关理论模型的观测边界。我们能始终保持领域领先地位的原因在于：坐拥南天球观测视野；拥有一支精干且聚焦核心目标的研究团队；配备了经过最优校准的接收系统；且能够以15至20天的近乎规则观测周期，在宽带宽条件下开展持续观测。通过本申请，我们旨在维持本领域的领先地位。

与多数观测申请不同，本申请属于持续性观测项目，相关观测将持续优化对超低频引力波（ultra-low-frequency gravitational waves）的约束边界，直至最终成功探测到这类引力波。Parkes望远镜的持续观测仍将具备重要科学价值，至少直至平方千米阵（Square Kilometre Array, SKA）第一阶段项目能够提升我们的观测灵敏度与观测周期为止。即便在非相干引力波背景被成功探测之后，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。