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arXiv 1007.3468astro-ph.CO
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用行星测量普朗克光束

Measuring Planck beams with planets

K. M. Huffenberger, B. P. Crill, A. E. Lange, K. M. Gorski, C. R. Lawrence

摘要:

精确测量宇宙微波背景(CMB)各向异性需要精确的仪器波束知识。我们探讨如何以及普朗克光束将确定从行星的观测,开发技术,也适用于其他实验。我们模拟行星观测与普朗克一样的扫描策略,望远镜光束,噪声和探测器的属性。然后,我们采用参数和非参数技术,重建光束直接从时间顺序的数据。通过对光束形状的忠实参数化,我们可以将某些探测器属性(例如探测器的时间常数)约束到高精度。或者,我们使用正交基分解光束。对于这两种技术,我们的特点与蒙特卡罗实现光束重建的错误。对于一个简化的扫描策略,我们研究的CMB功率谱估计的影响。最后,我们探讨了测量宇宙学参数的后果,重点是原始标量扰动的谱指数n_s。望远镜的光学建模将对功率谱测量的质量产生重要影响。在我们最保守的情况下,除了行星的测量之外,不使用任何关于光学的信息,我们发现木星穿过焦平面的单次凌日将测量对CMB最敏感的100-217 GHz通道的光束窗口函数优于0.3%。用光学建模来约束光束可以导致高得多的质量重建。根据光学模型,光束误差可能对n_s的测量系统有重要贡献。

英文摘要:

Accurate measurement of the cosmic microwave background (CMB) anisotropy requires precise knowledge of the instrument beam. We explore how well the Planck beams will be determined from observations of planets, developing techniques that are also appropriate for other experiments. We simulate planet observations with a Planck-like scanning strategy, telescope beams, noise, and detector properties. Then we employ both parametric and non-parametric techniques, reconstructing beams directly from the time-ordered data. With a faithful parameterization of the beam shape, we can constrain certain detector properties, such as the time constants of the detectors, to high precision. Alternatively, we decompose the beam using an orthogonal basis. For both techniques, we characterize the errors in the beam reconstruction with Monte Carlo realizations. For a simplified scanning strategy, we study the impact on estimation of the CMB power spectrum. Finally, we explore the consequences for measuring cosmological parameters, focusing on the spectral index of primordial scalar perturbations, n_s. The quality of the power spectrum measurement will be significantly influenced by the optical modeling of the telescope. In our most conservative case, using no information about the optics except the measurement of planets, we find that a single transit of Jupiter across the focal plane will measure the beam window functions to better than 0.3% for the channels at 100-217 GHz that are the most sensitive to the CMB. Constraining the beam with optical modeling can lead to much higher quality reconstruction. Depending on the optical modeling, the beam errors may be a significant contribution to the measurement systematics for n_s.

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