Parkes observations for project P1321 semester 2024APRS_05

We propose to search for temporal variations in HI absorption spectra seen against background pulsars to characterise Tiny Scale Atomic Structure (TSAS) in the Milky Way interstellar medium (ISM). We will re-observe seven previously studied bright pulsars at two observing epochs in this semester, resulting in minimum and maximum experimental baselines of 0.25 and 50 years. These observations will test predictions that there is a minimum size scale set by the thermal and turbulent properties of the ISM, below which TSAS is only sporadically seen, and will potentially provide the first direct measurements of pressures in "large" TSAS features of > 1000 AU. By using a new phase-resolved spectral line mode that we have recently implemented on Parkes, we will cut data rates and processing times by factors of ~1000. Following the success of this pilot project, we plan to expand to a long-term monitoring programme. Successful demonstration of our techniques will lay the groundwork for future programmes on the SKA.

本研究提出通过搜寻背景脉冲星的中性氢（HI）吸收光谱中的时间变化，以表征银河系星际介质（ISM）中的微尺度原子结构（Tiny Scale Atomic Structure，TSAS）。本计划将于本学期内的两个观测时段，重新观测7颗此前已被研究过的明亮脉冲星，其观测实验基线的最小与最大跨度分别为0.25年与50年。这些观测将验证一项理论预测：星际介质的热学与湍流特性限定了一个最小尺度阈值，低于该阈值的微尺度原子结构仅会偶发出现；同时本研究还有望首次直接测量尺度大于1000 AU的“大型”微尺度原子结构的压强。通过利用我们近期在帕克斯（Parkes）望远镜上部署的新型相位分辨谱线观测模式，我们可将数据速率与处理时长压缩约1000倍。在该先导项目取得成功后，我们计划将其拓展为长期监测计划。若本研究的技术方法得到验证，将为未来平方千米阵列（SKA）上的相关观测项目奠定基础。