Commissioning LOFAR for polarisation observations

用LOFAR这样的软件望远镜测量低频的线性极化射电辐射开辟了令人兴奋的科学前景，但在技术上具有挑战性。不动的望远镜元件的结构导致了高的仪器偏振，它随天空位置和距离光束中心的距离而变化，需要相当大的校正努力。此外，地球电离层的法拉第自转对于每个方向和每个LOFAR站都是不同的。成像软件需要考虑所有这些影响。到目前为止，可以在这个项目中识别和分析扭曲效应。开发了新的校准程序，产生了总强度的射电地图。几颗脉冲星和银河系一个区域的极化发射被成功探测到。这些调试工作将继续进行，并在未来几年完成。这些努力将由MPIfR的博士后进行，他们应该继续领导这些努力，并在技术问题上监督其他项目的学生。他应该得到阿尔法一名新的博士生的支持，该博士生应该开发偏振校准方法，包括仪器极化和电离层法拉第旋转的校正。

Measuring linearly polarised radio emission at low frequencies and with a software telescope such as LOFAR opens exciting scientific prospects, but is technically challenging. The construction of non-moving telescope elements results in high instrumental polarization which varies with position on the sky and with distance from the beam center and needs appreciable correction efforts. Furthermore, Faraday rotation in the Earth's ionosphere is different for each direction and for each LOFAR station. The imaging software needs to account for all of these effects. Until now the distorting effects could be identified and analysed in this project. New calibration procedures were developed, leading to radio maps in total intensity. Polarised emission from several pulsars and from a region in the Milky Way was successfully detected.These commissioning efforts are to be continued and finalised over the next years. These efforts shall be conducted by the postdoc at the MPIfR, who should continue to lead these efforts and supervise the students from the other projects in technical issues. He should be supported by a new PhD student at AlfA who should develop calibration methods for polarisation, including corrections for instrumental polarisation and ionospheric Faraday Rotation.