Polarization leakage in epoch of reionization windows - I. Low Frequency Array observations of the 3C196 field
Polarization leakage in epoch of reionization windows - I. Low Frequency Array observations of the 3C196 field
复制标题
再电离窗历元的极化泄漏 - I. 3C196 场的低频阵列观测
DOI：
10.1093/mnras/stv1107
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发表时间：
2015
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
来自再电离时期（EoR）的21-cm信号的检测是具有挑战性的，特别是因为，即使在去除前景之后，残留的StokesImaps包含来自可以模拟信号的偏振发射的泄漏。在这里，我们讨论了低频阵列（LOFAR）的仪器极化和斯托克斯参数之间的泄漏的现实模拟。从3C 196场中偏振辐射的LOFAR观测中，我们量化了LOFAR标称模型光束引起的偏振泄漏水平，并使用功率谱分析将其与EoR信号进行了比较。我们发现，在134-166 MHz时，在磁场中心4°范围内，（Q，U）→Ileakage功率低于EoR信号（k < 0.3 Mpc−1）。泄漏被发现是本地化周围的法拉第深度为0，和均方根的泄漏作为一个分数的均方根的极化发射被证明是在0.2%和0.3%之间变化，这两者都可以被利用在去除泄漏。此外，我们可以定义一个“EoR窗口”，即在点扩散函数（PSF）诱导的楔形之上和k = 0.5 Mpc−1之下的柱面功率谱中的偏振泄漏，当70%的泄漏被消除时，该窗口在所有k = 1时扩展到k = 1.1 Mpc− 1。这些LOFAR结果表明，即使在未来的阵列（如Square Kilometre Array）中，在104 °的视场内进行适度的偏振校准，也将确保偏振泄漏在0.02-1 Mpc−1的尺度下远低于预期的EoR信号。
Detection of the 21-cm signal coming from the epoch of reionization (EoR) is challenging especially because, even after removing the foregrounds, the residual StokesImaps contain leakage from polarized emission that can mimic the signal. Here, we discuss the instrumental polarization of Low Frequency Array (LOFAR) and present realistic simulations of the leakages between Stokes parameters. From the LOFAR observations of polarized emission in the 3C196 field, we have quantified the level of polarization leakage caused by the nominal model beam of LOFAR, and compared it with the EoR signal using power spectrum analysis. We found that at 134–166 MHz, within the central 4° of the field the (Q,U) →Ileakage power is lower than the EoR signal atk< 0.3 Mpc−1. The leakage was found to be localized around a Faraday depth of 0, and the rms of the leakage as a fraction of the rms of the polarized emission was shown to vary between 0.2 and 0.3 per cent, both of which could be utilized in the removal of leakage. Moreover, we could define an ‘EoR window’ in terms of the polarization leakage in the cylindrical power spectrum above the point spread function (PSF)-induced wedge and belowk∥∼ 0.5 Mpc−1, and the window extended up tok∥∼ 1 Mpc−1at allk⊥when 70 per cent of the leakage had been removed. These LOFAR results show that even a modest polarimetric calibration over a field of view of ≲ 4° in the future arrays like Square Kilometre Array will ensure that the polarization leakage remains well below the expected EoR signal at the scales of 0.02–1 Mpc−1.