Polarization leakage in epoch of reionization windows - II. Primary beam model and direction-dependent calibration
Polarization leakage in epoch of reionization windows - II. Primary beam model and direction-dependent calibration
复制标题
再电离窗口时代的偏振泄漏 - II。
DOI：
10.1093/mnras/stw1863
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发表时间：
2016
影响因子：
4.8
通讯作者：
Asad K
中科院分区：
文献类型：
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作者：
Asad K
由仪器的偏振主光束引起的扩散偏振辐射泄漏到斯托克斯I可能模仿来自再电离时代(EOR)的21厘米信号的光谱结构，使它们难以分离。因此，了解天线的极化性能对于成功检测提高采收率信号至关重要。在这里，我们计算了低频阵列标称模型波束(LOFAR)预测Stokes ItoQ，U泄漏的精度，并将它们与在3C-295场中实际观测到的紧凑源的相应泄漏进行了比较。我们发现，在视场范围内，模型光束对于≤1 Per Cent的泄漏预测水平的误差为∼10 Per Cent，也就是说，如果使用该模型完美地取出泄漏，则泄漏将减少到10−3的Stokes I通量。如果在消除Stokes Q，UtoI泄漏方面能够获得类似水平的精度，我们可以说，根据我们以前的论文的结果，使用这种波束模型消除这种泄漏将确保在几乎整个柱面功率谱的仪器空间内，泄漏远低于预期的EoR信号。我们还在这里表明，在给定一个非常接近本地噪声水平的非极化天空模型的情况下，依赖于方向的校准可以去除仪器极化的致密源。
Leakage of diffuse polarized emission into StokesIcaused by the polarized primary beam of the instrument might mimic the spectral structure of the 21-cm signal coming from the epoch of reionization (EoR) making their separation difficult. Therefore, understanding polarimetric performance of the antenna is crucial for a successful detection of the EoR signal. Here, we have calculated the accuracy of the nominal model beam of Low Frequency ARray (LOFAR) in predicting the leakage from StokesItoQ,Uby comparing them with the corresponding leakage of compact sources actually observed in the 3C 295 field. We have found that the model beam has errors of ≤10 per cent on the predicted levels of leakage of ∼1 per cent within the field of view, i.e. if the leakage is taken out perfectly using this model the leakage will reduce to 10−3of the StokesIflux. If similar levels of accuracy can be obtained in removing leakage from StokesQ,UtoI, we can say, based on the results of our previous paper, that the removal of this leakage using this beam model would ensure that the leakage is well below the expected EoR signal in almost the whole instrumentalk-space of the cylindrical power spectrum. We have also shown here that direction-dependent calibration can remove instrumentally polarized compact sources, given an unpolarized sky model, very close to the local noise level.