LSPE-SWIPE实验中偏振调制的优化策略
Optimal strategy for polarization modulation in the LSPE-SWIPE experiment
摘要：
CMB B模式实验需要以前所未有的准确度控制系统效应。半波片偏振调制是一种有效的技术，可以消除大量的仪器系统。我们的目标是优化即将到来的LSPE-SWIPE球载实验的偏振调制策略，致力于大角度尺度下CMB偏振的精确测量。我们离开标称LSPE-SWIPE调制策略（HWP步进每60秒，望远镜扫描速度约为12度/秒），并在频率，地图和角功率谱域中进行了广泛的可能的HWP方案（无论是在步进或连续旋转模式，并在不同的方位角望远镜扫描速度）的彻底调查。此外，我们探测的高通和带通滤波器的数据流的效果，并探讨HWP响应在最小的情况下，一个检测器的一个操作日（关键的单检测器校准过程）。我们最后测试的调制性能对典型的HWP诱导的系统。我们的分析表明，一些步进HWP计划，无论是缓慢旋转或与慢望远镜调制相结合，代表穷人的选择。此外，我们的结果指出，名义配置可能不是最方便的选择。虽然一大类旋转设计在像素角度覆盖、制图残差和BB功率谱标准偏差方面提供了与标称策略相当的结果，但我们发现一些特定配置（例如，具有慢吊舱调制的快速旋转HWP）允许在更一般的实际情况下更有效的偏振恢复。虽然我们的模拟是特定的LSPE-SWIPE任务，我们的分析的一般结果可以很容易地推广到其他CMB偏振实验。
英文摘要：
CMB B-mode experiments are required to control systematic effects with an unprecedented level of accuracy. Polarization modulation by a half wave plate (HWP) is a powerful technique able to mitigate a large number of the instrumental systematics. Our goal is to optimize the polarization modulation strategy of the upcoming LSPE-SWIPE balloon-borne experiment, devoted to the accurate measurement of CMB polarization at large angular scales. We depart from the nominal LSPE-SWIPE modulation strategy (HWP stepped every 60 s with a telescope scanning at around 12 deg/s) and perform a thorough investigation of a wide range of possible HWP schemes (either in stepped or continuously spinning mode and at different azimuth telescope scan-speeds) in the frequency, map and angular power spectrum domain. In addition, we probe the effect of high-pass and band-pass filters of the data stream and explore the HWP response in the minimal case of one detector for one operation day (critical for the single-detector calibration process). We finally test the modulation performance against typical HWP-induced systematics. Our analysis shows that some stepped HWP schemes, either slowly rotating or combined with slow telescope modulations, represent poor choices. Moreover, our results point out that the nominal configuration may not be the most convenient choice. While a large class of spinning designs provides comparable results in terms of pixel angle coverage, map-making residuals and BB power spectrum standard deviations with respect to the nominal strategy, we find that some specific configurations (e.g., a rapidly spinning HWP with a slow gondola modulation) allow a more efficient polarization recovery in more general real-case situations. Although our simulations are specific to the LSPE-SWIPE mission, the general outcomes of our analysis can be easily generalized to other CMB polarization experiments.
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