BeyondPlanck X. 带通和波束泄漏校正
BeyondPlanck X. Bandpass and beam leakage corrections
AI总结：
本文研究了BeyondPlanck CMB分析流水线中Planck LFI数据的带通与波束泄漏校正方法，通过对带通剖面进行多项预处理及参数拟合，显著降低了泄漏效应，并首次在Planck LFI地图中引入波束失配泄漏校正。
摘要：
我们讨论了在应用于Planck LFI测量的贝叶斯BeyondPlanck CMB分析流水线中，带通和波束泄漏校正的处理方法。作为准备步骤，我们首先对标称LFI带通剖面应用了三项校正，包括移除61 GHz地面测量设备中一个已知的系统效应；驻波波纹的平滑；以及边缘正则化。这些修改的主要净影响是70 GHz带通整体偏移了+0.6 GHz；我们认为任何对LFI数据产品的分析，无论是来自Planck还是BeyondPlanck，都应使用这些新带通。此外，我们为每个辐射计拟合一个自由带通参数，形式为$Δ_i = Δ_0 + δ_i$，其中$Δ_0$代表每个频带的绝对频率偏移，$δ_i$是每个探测器的相对偏移。绝对校正仅在30 GHz处使用基于$χ^2$的完整似然进行拟合，得到的校正为$Δ_{30}=0.24\pm0.03\\,$GHz。相对校正是使用伪图方法拟合的，在根本上与WMAP团队开创的方法类似，但没有引入许多额外的自由度。所有带通参数均使用标准Metropolis采样器在主BeyondPlanck Gibbs链内进行采样，因此带通不确定性被传播到分析中的所有其他数据产品。总而言之，我们发现我们的带通模型显著减少了泄漏效应。对于波束泄漏校正，我们采用官方的Planck LFI波束估计，没有额外的自由度，仅对底层天空模型进行边缘化。我们指出，这是首次在Planck LFI地图中包含波束失配引起的泄漏。
英文摘要：
We discuss the treatment of bandpass and beam leakage corrections in the Bayesian BeyondPlanck CMB analysis pipeline as applied to the Planck LFI measurements. As a preparatory step, we first apply three corrections to the nominal LFI bandpass profiles including removal of a known systematic effect in the ground measuring equipment at 61 GHz; smoothing of standing wave ripples; and edge regularization. The main net impact of these modifications is an overall shift in the 70 GHz bandpass of +0.6 GHz; we argue that any analysis of LFI data products, either from Planck or BeyondPlanck, should use these new bandpasses. In addition, we fit a single free bandpass parameter for each radiometer of the form $Δ_i = Δ_0 + δ_i$, where $Δ_0$ represents an absolute frequency shift per frequency band and $δ_i$ is a relative shift per detector. The absolute correction is only fitted at 30 GHz with a full $χ^2$-based likelihood, resulting in a correction of $Δ_{30}=0.24\pm0.03\,$GHz. The relative corrections are fitted using a spurious map approach, fundamentally similar to the method pioneered by the WMAP team, but without introducing many additional degrees of freedom. All bandpass parameters are sampled using a standard Metropolis sampler within the main BeyondPlanck Gibbs chain, and bandpass uncertainties are thus propagated to all other data products in the analysis. In total, we find that our bandpass model significantly reduces leakage effects. For beam leakage corrections, we adopt the official Planck LFI beam estimates without additional degrees of freedom, and only marginalize over the underlying sky model. We note that this is the first time leakage from beam mismatch has been included for Planck LFI maps.
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