Measurement of the Crab nebula polarization at 90 GHz as a calibrator for CMB experiments
Measurement of the Crab nebula polarization at 90 GHz as a calibrator for CMB experiments
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在 90 GHz 下测量蟹状星云偏振，作为 CMB 实验的校准器
DOI：
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发表时间：
2009
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通讯作者：
M. Tristram
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作者：
J. Aumont;L. Conversi;C. Thum;H. Wiesemeyer;E. Falgarone;J. Macías;F. Piacentini;E. Pointecouteau;N. Ponthieu;J. Puget;C. Rosset;J. Tauber;M. Tristram
旨在精确测量CMB偏振的CMB实验，例如普朗克卫星，需要在天空上安装强偏振绝对校准器，以便精确设置探测器的偏振角和交叉偏振泄漏。蟹状星云作为微波天空中角尺度为几弧分的最强烈的偏振源，将用于此目的。我们的目标是以前所未有的精度测量 90 GHz 的蟹状星云偏振特性。观测是使用 IRAM 30m 望远镜、相关偏振计 XPOL 和两个正交偏振接收器进行的。我们根据观测结果处理了 Stokes I、Q 和 U 图，以便计算偏振角和线性偏振分数。第一个在偏振最大发射区域几乎恒定，平均值为 alpha_Sky=152.1+/-0.2 度，第二个被发现对于大多数偏振像素达到最大值 Pi=30%。我们发现，具有 5 弧分圆形光束的 CMB 实验将看到平均偏振角 alpha_Sky=149.9+/-0.2 度和平均偏振分数 Pi=8.8+/-0.2%。
CMB experiments aiming at a precise measurement of the CMB polarization, such as the Planck satellite, need a strong polarized absolute calibrator on the sky in order to accurately set the detectors polarization angle and the cross-polarization leakage. The Crab Nebula, as the most intense polarized source in the microwave sky at angular scales of few arcminutes, will be used for this purpose. Our goal was to measure the Crab nebula polarization characteristics at 90 GHz with an unprecedented precision. The observations were carried out with the IRAM 30m telescope employing the correlation polarimeter XPOL and using two orthogonally polarized receivers. We have processed the Stokes I, Q and U maps from our observations in order to compute the polarization angle and linear polarization fraction. The first is almost constant in the region of maximum emission in polarization with a mean value of alpha_Sky=152.1+/-0.2 deg and the second is found to reach a maximum of Pi=30% for the most polarized pixels. We find that a CMB experiment having a 5 arcmin circular beam will see a mean polarization angle of alpha_Sky=149.9+/-0.2 deg and a mean polarization fraction of Pi=8.8+/-0.2%.