Comparing Redundant and Sky-model-based Interferometric Calibration: A First Look with Phase II of the MWA
Comparing Redundant and Sky-model-based Interferometric Calibration: A First Look with Phase II of the MWA
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DOI：
10.3847/1538-4357/aad3c3
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发表时间：
2018-07
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通讯作者：
W. Li;J. Pober;B. Hazelton;N. Barry;M. Morales;I. Sullivan;A. Parsons;Z. Ali;J. Dillon;A. Beardsley;J. Bowman;F. Briggs;R. Byrne;P. Carroll;B. Crosse;D. Emrich;A. Ewall-Wice;L. Feng;T. Franzen;J. Hewitt;L. Horsley;D. Jacobs;M. Johnston-Hollitt;C. Jordan;R. Joseph;D. Kaplan;D. Kenney;H. Kim;P. Kittiwisit;A. Lanman;J. Line;B. McKinley;D. Mitchell;S. Murray;A. Neben;A. Offringa;D. Pallot;S. Paul;B. Pindor;P. Procopio;M. Rahimi;J. Riding;S. Sethi;N. Shankar;K. Steele;R. Subrahmanian;Max Tegmark;N. Thyagarajan;S. Tingay;C. Trott;M. Walker;R. Wayth;R. Webster;A. Williams;C. Wu;S. Wyithe
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作者：
W. Li;J. Pober;B. Hazelton;N. Barry;M. Morales;I. Sullivan;A. Parsons;Z. Ali;J. Dillon;A. Beardsley;J. Bowman;F. Briggs;R. Byrne;P. Carroll;B. Crosse;D. Emrich;A. Ewall-Wice;L. Feng;T. Franzen;J. Hewitt;L. Horsley;D. Jacobs;M. Johnston-Hollitt;C. Jordan;R. Joseph;D. Kaplan;D. Kenney;H. Kim;P. Kittiwisit;A. Lanman;J. Line;B. McKinley;D. Mitchell;S. Murray;A. Neben;A. Offringa;D. Pallot;S. Paul;B. Pindor;P. Procopio;M. Rahimi;J. Riding;S. Sethi;N. Shankar;K. Steele;R. Subrahmanian;Max Tegmark;N. Thyagarajan;S. Tingay;C. Trott;M. Walker;R. Wayth;R. Webster;A. Williams;C. Wu;S. Wyithe
干涉测量阵列要想测量再电离时代（EOR）的21厘米信号，就必须与前景源的极亮发射相抗衡。准确恢复21厘米信号需要对阵列进行精确校准，近年来已经采用了几种新的校准方法，包括在天线配置中使用冗余的方法。新升级的Murchison宽场阵列（MWA）二期是第一个具有大量冗余基线的干涉仪，同时保持良好的瞬时紫外线覆盖。因此，这个阵列提供了一个独特的机会来比较冗余校准与基于天空模型的算法。在本文中，我们将两种校准方法与MWA II期观测结果进行了比较。对于冗余校准，我们使用omnic包，并使用快速全息反褶积（FHD）分析包生成基于天空的校准解决方案。主要有三个结果：(1)我们报告了omnic在ORBComm卫星观测上的成功，显示了校准后冗余能见度测量之间的基本一致。(2)我们直接比较了omnic校准方案和FHD的校准方案，并证明这两种不同的校准方案给出了非常相似的结果。(3)结合omnic和FHD，探索改进的校准方法。我们使用为提高采收率分析开发的功率谱技术对这些组合方法进行了评估，并找到了边际改进的证据，减轻了功率谱中的伪影。这些结果可能受到6小时所用数据的信噪比的限制，但它们为结合这两种校准方案提出了未来的方向。
Interferometric arrays seeking to measure the 21 cm signal from the epoch of reionization (EOR) must contend with overwhelmingly bright emission from foreground sources. Accurate recovery of the 21 cm signal will require precise calibration of the array, and several new avenues for calibration have been pursued in recent years, including methods using redundancy in the antenna configuration. The newly upgraded Phase II of Murchison Widefield Array (MWA) is the first interferometer that has large numbers of redundant baselines while retaining good instantaneous UV coverage. This array therefore provides a unique opportunity to compare redundant calibration with sky-model-based algorithms. In this paper, we present the first results from comparing both calibration approaches with MWA Phase II observations. For redundant calibration, we use the package OMNICAL and produce sky-based calibration solutions with the analysis package Fast Holographic Deconvolution (FHD). There are three principal results: (1) We report the success of OMNICAL on observations of ORBComm satellites, showing substantial agreement between redundant visibility measurements after calibration. (2) We directly compare OMNICAL calibration solutions with those from FHD and demonstrate that these two different calibration schemes give extremely similar results. (3) We explore improved calibration by combining OMNICAL and FHD. We evaluate these combined methods using power spectrum techniques developed for EOR analysis and find evidence for marginal improvements mitigating artifacts in the power spectrum. These results are likely limited by the signal-to-noise ratio in the 6 hr of data used, but they suggest future directions for combining these two calibration schemes.