The impact of interference excision on 21-cm epoch of reionization power spectrum analyses
The impact of interference excision on 21-cm epoch of reionization power spectrum analyses
复制标题
干扰消除对 21 cm 历元再电离功率谱分析的影响
DOI：
10.1093/mnras/stz175
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发表时间：
2019
影响因子：
4.8
通讯作者：
L. Koopmans
中科院分区：
文献类型：
--
作者：
A. Offringa;A. Offringa;Florent Mertens;L. Koopmans
我们调查的影响，干扰检测的实验正在追求的红移21厘米信号的再电离时代（EoR）的检测。干扰检测导致样本偶尔被标记和拒绝。为了减少数据量，标记的样本通常在时间或频率平均或UV网格化期间（隐式地）内插。这是迄今为止尚未探索的21厘米功率谱的系统偏差，重要的是要了解目前的21厘米实验以及即将到来的平方公里阵列EoR实验的这种偏差。我们使用功率谱分析和高斯过程回归分析模拟数据。我们发现，标记和平均的结合会导致微小的光谱波动，从而导致“标记多余功率”。这种多余的功率不会随着时间的推移而平均下来，如果没有额外的缓解技术，可以超过低频阵列（LOFAR）观测中21厘米再电离信号的现实模型的功率。我们通过（i）使用高斯加权插值方案实现一种新的方法来平均数据，（ii）使用酉而不是逆方差加权的vibration，以及（iii）使用低分辨率的数据正演建模来减轻偏差。在这些修改之后，这些修改已经集成到LOFAR EoR处理管道中，多余的功率减少了大约三个数量级，并且不再阻止21 cm信号的检测。
We investigate the implications of interference detection for experiments that are pursuing a detection of the redshifted 21-cm signals from the epoch of reionization (EoR). Interference detection causes samples to be sporadically flagged and rejected. As a necessity to reduce the data volume, flagged samples are typically (implicitly) interpolated during time or frequency averaging or uv-gridding. This so-far unexplored systematic biases of the 21-cm power spectrum, and it is important to understand this bias for current 21-cm experiments as well as the upcoming Square Kilometre Array EoR experiment. We analyse simulated data using power spectrum analysis and Gaussian process regression. We find that the combination of flagging and averaging causes tiny spectral fluctuations, resulting in 'flagging excess power'. This excess power does not substantially average down overtime and, without extra mitigation techniques, can exceed the power of realistic models of the 21-cm reionization signals in Low-Frequency Array (LOFAR) observations. We mitigate the bias by (i) implementing a novel way to average data using a Gaussian-weighted interpolation scheme, (ii) using unitary instead of inverse variance weighting of visibilities, and (iii) using low-resolution forward modelling of the data. After these modifications, which have been integrated in the LOFAR EoR processing pipeline, the excess power reduces by approximately three orders of magnitude, and is no longer preventing a detection of the 21-cm signals.
影响因子：
6.5
作者：
van Haarlem, M. P.;Wise, M. W.;van Zwieten, J.
通讯作者：
van Zwieten, J.