The HERA-19 Commissioning Array: Direction-dependent Effects
The HERA-19 Commissioning Array: Direction-dependent Effects
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DOI：
10.3847/1538-4357/ab2f72
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发表时间：
2018-02
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通讯作者：
S. Kohn;J. Aguirre;P. Plante;T. Billings;P. Chichura;A. F. Fortino;A. Igarashi;Roshan K. Benefo;S. Gallardo;Z. Martinot;C. Nunhokee;N. Kern;P. Bull;Adrian Liu;P. Alexander;Z. Ali;A. Beardsley;G. Bernardi;J. Bowman;R. Bradley;C. Carilli;Carina Cheng;D. DeBoer;E. D. L. Acedo;J. Dillon;A. Ewall-Wice;G. Fadana;N. Fagnoni;Randall Fritz;S. Furlanetto;B. Glendenning;B. Greig;J. Grobbelaar;B. Hazelton;J. Hewitt;J. Hickish;D. Jacobs;A. Julius;M. Kariseb;M. Kolopanis;Telalo Lekalake;A. Loots;D. MacMahon;Lourence Malan;Cresshim Malgas;M. Maree;Nathan Mathison;Eunice Matsetela;A. Mesinger;M. Morales;A. Neben;B. Nikolic;A. Parsons;Nipanjana Patra;Samantha Pieterse;J. Pober;N. Razavi-Ghods;J. Ringuette;J. Robnett;K. Rosie;R. Sell;Craig H. Smith;A. Syce;Max Tegmark;N. Thyagarajan;P. Williams;Haoxuan Zheng
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作者：
S. Kohn;J. Aguirre;P. Plante;T. Billings;P. Chichura;A. F. Fortino;A. Igarashi;Roshan K. Benefo;S. Gallardo;Z. Martinot;C. Nunhokee;N. Kern;P. Bull;Adrian Liu;P. Alexander;Z. Ali;A. Beardsley;G. Bernardi;J. Bowman;R. Bradley;C. Carilli;Carina Cheng;D. DeBoer;E. D. L. Acedo;J. Dillon;A. Ewall-Wice;G. Fadana;N. Fagnoni;Randall Fritz;S. Furlanetto;B. Glendenning;B. Greig;J. Grobbelaar;B. Hazelton;J. Hewitt;J. Hickish;D. Jacobs;A. Julius;M. Kariseb;M. Kolopanis;Telalo Lekalake;A. Loots;D. MacMahon;Lourence Malan;Cresshim Malgas;M. Maree;Nathan Mathison;Eunice Matsetela;A. Mesinger;M. Morales;A. Neben;B. Nikolic;A. Parsons;Nipanjana Patra;Samantha Pieterse;J. Pober;N. Razavi-Ghods;J. Ringuette;J. Robnett;K. Rosie;R. Sell;Craig H. Smith;A. Syce;Max Tegmark;N. Thyagarajan;P. Williams;Haoxuan Zheng
前景功率在干涉仪的测量中占据主导地位，这些干涉仪寻求对再电离期（EoR）的高度红移H i发射进行统计检测。仪器的色度在频率的傅里叶变换中（与k π成比例）在光谱平滑发射（强同步加速器前景的特征（“楔形”））和来自EoR中的H i的光谱结构化发射（“EoR窗口”）之间产生边界。法拉第旋转可以将光谱结构注入到原本平滑的偏振前景发射中，其通过仪器效应或误校准可能污染EoR窗口。对于追求简单地在EoR窗口中进行测量的“前景避免”策略的仪器，并且不试图建模和去除前景，正如再电离阵列（HERA）的氢时代的第一阶段的计划一样，表征仪器的固有偏振响应是特别重要的。使用HERA 19元件调试阵列的数据，我们调查了这种新仪器在功率谱域的偏振响应。我们进行了一个简单的基于图像的校准的基础上的非偏振漫射发射的全球天空模型，并表明，它实现了定性冗余之间的名义上冗余基线的阵列和合理的幅度精度。我们构建功率谱的所有全偏振相干在所有的伪斯托克斯参数，并讨论了实现隔离的前景功率由于固有的光谱平滑的前景，仪器的色度，和校准。我们比较模拟的基础上的非偏振漫射天空模型和详细的电磁模拟的菜和饲料，确认在斯托克斯我，校准不增加显着的光谱结构超出预期的干涉仪阵列配置和建模的初级光束响应。此外，该校准在所考虑的8天观察期间是稳定的。过剩的功率被认为是在功率谱的线性偏振斯托克斯参数，这是不容易归因于泄漏通过初级光束，并从一些组合的残余校准误差和实际的偏振发射的结果。斯托克斯V被发现是高度不一致的零功率的期望，强烈指向需要更准确的偏振校准。
Foreground power dominates the measurements of interferometers that seek a statistical detection of highly-redshifted H i emission from the Epoch of Reionization (EoR). The chromaticity of the instrument creates a boundary in the Fourier transform of frequency (proportional to k∥) between spectrally smooth emission, characteristic of the strong synchrotron foreground (the “wedge”), and the spectrally structured emission from H i in the EoR (the “EoR window”). Faraday rotation can inject spectral structure into otherwise smooth polarized foreground emission, which through instrument effects or miscalibration could possibly pollute the EoR window. For instruments pursuing a “foreground avoidance” strategy of simply measuring in the EoR window, and not attempting to model and remove foregrounds, as is the plan for the first stage of the Hydrogen Epoch of Reionization Array (HERA), characterizing the intrinsic instrument polarization response is particularly important. Using data from the HERA 19-element commissioning array, we investigate the polarization response of this new instrument in the power-spectrum domain. We perform a simple image-based calibration based on the unpolarized diffuse emission of the Global Sky Model, and show that it achieves qualitative redundancy between the nominally redundant baselines of the array and reasonable amplitude accuracy. We construct power spectra of all fully polarized coherencies in all pseudo-Stokes parameters, and discuss the achieved isolation of foreground power due to the intrinsic spectral smoothness of the foregrounds, the instrument chromaticity, and the calibration. We compare to simulations based on an unpolarized diffuse sky model and detailed electromagnetic simulations of the dish and feed, confirming that in Stokes I, the calibration does not add significant spectral structure beyond that expected from the interferometer array configuration and the modeled primary beam response. Furthermore, this calibration is stable over the 8 days of observations considered. Excess power is seen in the power spectra of the linear polarization Stokes parameters, which is not easily attributable to leakage via the primary beam, and results from some combination of residual calibration errors and actual polarized emission. Stokes V is found to be highly discrepant from the expectation of zero power, strongly pointing to the need for more accurate polarized calibration.