Analytic approximations of scattering effects on beam chromaticity in 21-cm global experiments
Alan E. E. Rogers, John P. Barrett, Judd D. Bowman, Rigel Cappallo, Colin J. Lonsdale, Nivedita Mahesh, Raul A. Monsalve, Steven G. Murray, Peter H. Sims
Scattering from objects near an antenna produce correlated signals from strong compact radio sources in a manner similar to those used by the Sea Interferometer to measure the radio source positions using the fine frequency structure in the total power spectrum of a single antenna. These fringes or ripples due to correlated signal interference are present at a low level in the spectrum of any single antenna and are a major source of systematics in systems used to measure the global redshifted 21-cm signal from the early universe. In the Sea Interferometer a single antenna on a cliff above the sea is used to add the signal from the direct path to the signal from the path reflected from the sea thereby forming an interferometer. This was used for mapping radio sources with a single antenna by Bolton and Slee in the 1950s. In this paper we derive analytic expressions to determine the level of these ripples and compare these results in a few simple cases with electromagnetic modeling software to verify that the analytic calculations are sufficient to obtain the magnitude of the scattering effects on the measurements of the global 21-cm signal. These analytic calculations are needed to evaluate the magnitude of the effects in cases that are either too complex or take too much time to be modeled using software.
A Bayesian approach to modelling spectrometer data chromaticity corrected using beam factors -- II. Model priors and posterior odds
Arizona State University（亚利桑那州立大学）；Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, UK（剑桥大学卡文迪许实验室）；Kavli Institute for Cosmology, Madingley Road, Cambridge CB3 0HA, UK（卡弗里宇宙学研究所）；Scuola Normale Superiore (SNS)（比萨高等师范学院）；MIT Haystack Observatory（麻省理工学院海斯塔克天文台）；California Institute of Technology（加州理工学院）；Space Sciences Laboratory, University of California Berkeley（加州大学伯克利分校空间科学实验室）；Universidad Católica de la Santísima Concepción（天主教神圣感学院）
Robust Extraction of Global 21 cm Spectrum from Experiments with a Chromatic Beam Based on Physics-Motivated Error Modeling
State Key Laboratory of Radio Astronomy and Technology, National Astronomical Observatories, CAS（射电天文科学与技术国家重点实验室，中国科学院国家天文台）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）
A General Bayesian Framework for Foreground Modelling and Chromaticity Correction for Global 21cm Experiments
HI 21 cm吸收线被明亮的前景和系统失真所掩盖，这些失真是由于用于使观测耦合到这些前景的光谱不均匀性的天线的色度而产生的。我们证明，这些失真是足以掩盖21厘米的信号时，天线是不完美的消色差和简单的校正假设一个恒定的空间分布的前景功率是不足以克服它们。然后，我们提出了一个新的物理动机的方法建模的前景21厘米的实验，以适应作为前景的一部分，色彩失真。这是通过将天空划分为$N$区域并在每个区域中假设不同的均匀光谱指数来缩放底图来生成跨观测波段的模拟天空模型来完成的。然后，可以将得到的天空图与天线波束模型进行卷积，以给出由$N$区域的光谱指数参数化的前景和色度模型。我们证明，拟合此模型的不同$N$使用贝叶斯嵌套抽样算法和比较结果使用的证据允许21厘米的信号被可靠地检测到的数据中的一个相对平滑的圆锥形日志螺旋天线。我们还测试了一个更彩色圆锥形正弦天线，发现这个模型不会产生一个可靠的信号检测，但在一种方式，很容易区分从一个真正的检测。
Formulating and critically examining the assumptions of global 21-cm signal analyses: How to avoid the false troughs that can appear in single spectrum fits
Blade Antenna-SDR System Prototype for the CANTAR Global 21-cm Experiment: Simulations, Measurements, and In-Situ Results
Universidad Industrial de Santander（桑坦德工业大学）；Fundación para el Desarrollo de la Radioastronomía y Tecnologías Aplicadas - FUDARTA（射电天文与应用技术发展基金会）；Universidad ECCI（ECCI大学）
