Calibrating high-precision Faraday rotation measurements for LOFAR and the next generation of low-frequency radio telescopes
Calibrating high-precision Faraday rotation measurements for LOFAR and the next generation of low-frequency radio telescopes
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DOI：
10.1051/0004-6361/201220728
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发表时间：
2013-03
影响因子：
6.5
通讯作者：
C. Sotomayor-Beltran;C. Sobey;J. Hessels;G. D. Bruyn;A. Noutsos;A. Alexov;J. Anderson;A. Asgekar-A.-Asg
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文献类型：
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作者：
C. Sotomayor-Beltran;C. Sobey;J. Hessels;G. D. Bruyn;A. Noutsos;A. Alexov;J. Anderson;A. Asgekar-A.-Asg
使用当前和下一代低频射电望远镜进行的法拉第旋转测量将为天文磁场提供强有力的探测。然而，实现这些测量的全部潜力，需要准确地去除时变电离层法拉第旋转的贡献。我们提出了ionFR，计算电离层法拉第旋转量的代码为一个特定的时代，地理位置和视线。ionFR使用了一些公开的、GPS衍生的总电子含量地图和最新发布的国际地磁参考场。我们描述的应用程序的无线电极化观测的校准，并证明其建模电离层法拉第旋转使用LOFAR脉冲星观测的高精度。这些表明，我们可以准确地确定一些有史以来最高精度的脉冲星旋转措施。精确的旋转测量可以用来监测旋转测量的变化-无论是内在的还是由于星际介质中视线的变化而引起的。这种校准对于附近的源特别重要，因为电离层可以对观测到的旋转测量做出很大的贡献。我们还讨论了ionFR计划的改进，以及电离层法拉第旋转校准的重要性，为新兴的一代低频射电望远镜，如SKA及其探路者。
Faraday rotation measurements using the current and next generation of low-frequency radio telescopes will provide a powerful probe of astronomical magnetic fields. However, achieving the full potential of these measurements requires accurate removal of the time-variable ionospheric Faraday rotation contribution. We present ionFR, a code that calculates the amount of ionospheric Faraday rotation for a specific epoch, geographic location, and line-of-sight. ionFR uses a number of publicly available, GPS-derived total electron content maps and the most recent release of the International Geomagnetic Reference Field. We describe applications of this code for the calibration of radio polarimetric observations, and demonstrate the high accuracy of its modeled ionospheric Faraday rotations using LOFAR pulsar observations. These show that we can accurately determine some of the highest-precision pulsar rotation measures ever achieved. Precision rotation measures can be used to monitor rotation measure variations - either intrinsic or due to the changing line-of-sight through the interstellar medium. This calibration is particularly important for nearby sources, where the ionosphere can contribute a significant fraction of the observed rotation measure. We also discuss planned improvements to ionFR, as well as the importance of ionospheric Faraday rotation calibration for the emerging generation of low-frequency radio telescopes, such as the SKA and its pathfinders.