发表机构
Ghana Space Science and Technology Institute Ghana Atomic Energy Commission; University of California Santa Cruz; University of Nigeria Nsukka（加纳空间科学与研究所 加纳原子能委员会; 加州大学圣克鲁兹分校; 尼日利亚恩苏卡大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过GRASP电磁模拟，在5.0和6.7 GHz下建立了GRAO 32米望远镜的定量偏振波束模型，评估了波束形状、泄漏和IXR，为方向相关校准提供了基线。
AI 中文摘要
方向相关的仪器偏振是高保真单碟射电偏振测量中的一个主要系统性限制，然而对于加纳射电天文台（GRAO）32米望远镜，缺乏对波束泄漏和偏振恢复条件的统一表征。我们旨在5.0和6.7 GHz频率下建立一个定量的、方向相关的偏振波束模型。使用标称望远镜配置的高分辨率\ exttt{GRASP}电磁模拟来推导完整的复琼斯响应和相应的穆勒矩阵，据此在主波束范围内评估波束形状、波束斜视、仪器斯托克斯泄漏和固有交叉极化比（IXR）。斯托克斯$I$波束在5.0和6.7 GHz下的半功率波束宽度分别为$396.4$和$295.3$角秒，主波束效率分别为$56.4\%$和$55.6\%$。在5.0 GHz下，圆极化波束斜视为$9.96$角秒（占HPBW的$2.5\%$），而在6.7 GHz下未检测到统计显著的斜视。斯托克斯$I$到线极化的泄漏在半功率波束内保持在$0.1\%$以下，但向旁瓣方向显著增加。IXR在轴上达到约$80$ dB，并随角偏移而减小。这些结果确立了GRAO 32米望远镜的固有电磁偏振响应，并为方向相关的校准和后续观测验证提供了定量基线。
英文摘要
Direction-dependent instrumental polarisation is a major systematic limitation in high-fidelity single-dish radio polarimetry, yet a unified characterisation of beam leakage and the conditioning of polarisation recovery is lacking for the Ghana Radio Astronomy Observatory (GRAO) 32-m telescope. We aim to establish a quantitative, direction-dependent polarimetric beam model at 5.0 and 6.7 GHz. High-resolution \texttt{GRASP} electromagnetic simulations of the nominal telescope configuration are used to derive the full complex Jones response and corresponding Mueller matrices, from which beam shape, beam squint, instrumental Stokes leakage, and intrinsic cross-polarisation ratio (IXR) are evaluated across the primary beam. The Stokes $I$ beams have half-power beam widths of $396.4$ and $295.3$ arcsec at 5.0 and 6.7 GHz, respectively, with main-beam efficiencies of $56.4$ and $55.6$ per cent. At 5.0 GHz, the circular-polarisation beam squint is $9.96$ arcsec ($2.5$ per cent of the HPBW), whereas no statistically significant squint is detected at 6.7 GHz. Leakage from Stokes $I$ into linear polarisation remains below $0.1$ per cent within the half-power beam but increases substantially towards the sidelobes. IXR reaches approximately $80$ dB on axis and decreases with angular offset. These results establish the intrinsic electromagnetic polarimetric response of the GRAO 32-m telescope and provide a quantitative baseline for direction-dependent calibration and subsequent observational validation.
Comments20 pages, 12 figures, 3 tables, accepted to RASTI
