EDGES低频天线波束模型的验证
Validation of EDGES Low-Band Antenna Beam Model
摘要：
天线的响应是全球EoR特征探测实验（EDGES）测量的不确定性来源。我们的目标是验证波束模型的低频段（50-100 MHz）偶极天线与模型之间的比较和对数据。我们发现，一个简化的模型的天线在一个无限的完美的导电接地平面的模拟，有一个例外，强大的数值电磁求解器代码或算法的变化。对于天线与实际有限的接地平面和现实的土壤属性的模拟，我们发现，三个数值求解器中的两个同意。将我们的分析管道应用于早期EDGES低波段仪器的模拟漂移扫描观测，该仪器具有10 m $\times$ 10 m接地平面，我们发现拟合和删除五项前景模型后的残留水平，以本地恒星时（LST）平均约250 mK的数据分组，数值求解器之间的$\pm$ 40 mK变化。对主30 m $\times$ 30 m接地层进行的类似分析将LST平均残差降至约90 mK，两个可行解算器之间的$\pm$为10 mK。更广泛地说，我们表明，较大的接地平面通常比较小的接地平面表现更好。模拟数据的功率在实际观测值的4 $\%$以内，这是天空和波束模型净精度的限制。我们观察到，残留的光谱结构后，前景模型拟合模拟数据和观测之间的定性匹配，这表明光束的频率依赖性是合理的模型表示。我们发现，0.02钐$^{-1}$和相对介电常数为3.5的土壤电导率产生良好的模拟光谱和观测之间的协议。这与Sutinjo等人（2015年）报告的Murchison射电天文台（EDGES所在地）的土壤特性一致。
英文摘要：
The response of the antenna is a source of uncertainty in measurements with the Experiment to Detect the Global EoR Signature (EDGES). We aim to validate the beam model of the low-band (50-100 MHz) dipole antenna with comparisons between models and against data. We find that simulations of a simplified model of the antenna over an infinite perfectly conducting ground plane are, with one exception, robust to changes of numerical electromagnetic solver code or algorithm. For simulations of the antenna with the actual finite ground plane and realistic soil properties, we find that two out of three numerical solvers agree well. Applying our analysis pipeline to a simulated driftscan observation from an early EDGES low-band instrument that had a 10 m $\times$ 10 m ground plane, we find residual levels after fitting and removing a five-term foreground model to data binned in Local Sidereal Time (LST) average about 250 mK with $\pm$40 mK variation between numerical solvers. A similar analysis of the primary 30 m $\times$ 30 m sawtooth ground plane reduced the LST-averaged residuals to about 90 mK with $\pm$10 mK between the two viable solvers. More broadly we show that larger ground planes generally perform better than smaller ground planes. Simulated data have a power which is within 4$\%$ of real observations, a limitation of net accuracy of the sky and beam models. We observe that residual spectral structures after foreground model fits match qualitatively between simulated data and observations, suggesting that the frequency dependence of the beam is reasonably represented by the models. We find that soil conductivity of 0.02 Sm$^{-1}$ and relative permittivity of 3.5 yield good agreement between simulated spectra and observations. This is consistent with the soil properties reported by Sutinjo et al. (2015) for the Murchison Radio-astronomy Observatory, where EDGES is located.
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