HIRAX的天线组装精度
Dish Assembly Precision for HIRAX
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中文总结 AI 辅助
本文研究正在南非部署的HIRAX射电干涉仪首批28台天线的组装精度，发现馈源定位精密度待提升，其结果为建模主波束效应、减轻HI IM信号系统误差提供基准。
中文摘要 AI 辅助
氢强度与实时分析实验（Hydrogen Intensity and Real-time Analysis eXperiment，HIRAX）是一台正在南非射电天文台（South African Radio Astronomy Observatory，SARAO）平方公里阵列（Square Kilometer Array，SKA）站点部署的射电干涉仪阵列，旨在测绘南天，通过强度映射（Intensity Mapping，IM）观测红移范围0.78-2.55的中性氢（neutral hydrogen，HI）。对HI的观测可层析探测大尺度宇宙体积，进而约束暗能量状态方程等宇宙学参数。由于存在强前景信号，系统误差是从HI IM推导宇宙学约束的重要问题，需严格控制和监测天线表面偏差、馈源定位误差等仪器效应，以维持HIRAX冗余阵列配置的灵敏度，这些仪器系统误差会导致明亮的前景功率泄漏到微弱的宇宙信号中。该阵列的6米抛物面天线采用嵌入铝网的玻璃纤维制成，铝网作为反射器；馈源通过4根玻璃纤维支腿固定在主焦点（f/D=0.21）处。本文基于天线制造期间的摄影测量计量学测量及现场测量，给出首批28台天线的表面和馈源定位精度：表面偏差大多符合要求，馈源定位满足所有精度标准但未达精密度限值，不过预计更大样本量可提升精密度。这些结果为建模主波束效应奠定了基准，最终可通过完整HIRAX阵列表征并减轻HI IM信号中的系统误差。
英文摘要
The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is a radio interferometer array that is being deployed at the South African Radio Astronomy Observatory (SARAO) Square Kilometer Array (SKA) site in South Africa. Mapping the southern sky, its aim is to observe neutral hydrogen (HI) through intensity mapping (IM) across the redshift range of 0.78-2.55. The observation of HI makes it possible to tomographically probe large cosmological volumes, enabling constraints on, for example, the dark energy equation of state. Systematics are a significant concern in deriving cosmological constraints from HI IM due to the presence of strong foreground signals. Instrumental effects such as dish surface deviations and feed placement errors need to be carefully controlled and monitored to preserve the sensitivity of HIRAX's redundant array configuration. These instrumental systematics cause bright foreground power to leak into the faint cosmological signal. The 6 m parabolic dishes are made from fiberglass with an embedded aluminum mesh that acts as the reflector. The feed is held in place at the prime focus (f/D = 0.21) by four fiberglass legs. This paper presents the dish surface and feed placement precision of the first 28 dishes, derived from photogrammetry metrology measurements taken during the dish fabrication, as well as from measurements in the field. While surface deviations are predominantly well within requirements, feed placement satisfies all accuracy criteria but fails precision limits; however, precision is expected to improve with a larger sample size. These results establish a baseline for modeling primary beam effects, ultimately enabling the characterization and mitigation of systematic errors in the HI IM signal with the full HIRAX array.
