Parkes observations for project P456 semester 2021APRS_01

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!帕克斯脉冲星计时阵列（Parkes Pulsar Timing Array，PPTA）项目拥有三大核心目标：（a）探测各类天文源产生的引力波，（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。我们虽配备规模最小的望远镜与研究群组，但取得了最为精密的测量数据与最出色的科研成果。我们针对非相干引力波背景强度给出的约束，是目前唯一可对相关理论模型形成有效限制的约束条件。我们能够始终保持领域领先地位的原因在于：我们拥有得天独厚的南天区观测视角；我们拥有一支规模小巧但目标高度聚焦的研究团队；我们配备了经过最优校准的射电接收机；并且我们能够以15至20天的近乎规则观测频次，在宽带宽范围内开展持续观测。通过本提案，我们旨在巩固本领域的领军地位。 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对超低频引力波的约束精度，直至最终成功探测到该信号。至少在平方千米阵（Square Kilometre Array，SKA）第一阶段建成并实现更高的探测灵敏度与观测节奏优化之前，帕克斯天文台的持续观测仍将具备极高科研价值。即便非相干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发展！