Parkes observations for project P1321 semester 2024OCTS_03

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. This project successfully observed in 2024APR and will be expanded to a Long Term Project when that scheme reopens for applications in 2025APR. 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射电辐射穿过星际介质时产生的中性氢（HI）吸收谱的时间变化特征，以表征银河系星际介质（ISM）中的小尺度原子结构（TSAS）。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范围为0.25年至50年。此次观测将验证一项理论预言：星际介质的热学与湍流特性设定了一个最小尺寸尺度，当结构尺寸小于该尺度时，小尺度原子结构仅会零星出现；同时本项目还有望首次直接测得尺寸大于1000天文单位（AU）的‘大型’小尺度原子结构的压强。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耗时压缩约1000倍。本项目已于2024年4月完成成功观测，并将于2025年4月该项目开放申请时，扩展为长期项目。本项目技术的成功验证，将为后续平方千米阵列（SKA）相关观测项目奠定基础。