Parkes observations for project P1321 semester 2024APRS_07

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.

本研究拟通过搜寻观测背景脉冲星时所得中性氢（HI）吸收谱的时间变化特征，对银河系星际介质（Interstellar Medium, ISM）中的小尺度原子结构（Tiny Scale Atomic Structure, TSAS）进行表征。本项目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，由此得到的实验基线时长跨度为0.25年至50年。此次观测将对一项理论预言进行检验：星际介质的热学与湍流特性设定了一个最小尺寸阈值，小于该阈值的小尺度原子结构仅会被零星观测到；同时本项目还有望首次直接测量大于1000天文单位（Astronomical Unit, AU）的"large"小尺度原子结构特征的压强。通过使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，本项目可将数据速率与处理时间压缩约1000倍。待本先导项目取得成功后，我们计划将研究拓展至长期监测项目。本项目所用技术的成功验证，将为未来在平方公里阵列望远镜（Square Kilometre Array, SKA）上开展的相关科研项目奠定坚实基础。