用平方公里阵列低前兆解决低频太阳偏振测量的独特挑战：算法
Tackling the Unique Challenges of Low-frequency Solar Polarimetry with the Square Kilometre Array Low Precursor: The Algorithm
摘要：
众所周知，日冕磁场是定义日冕物理和空间天气的关键参数之一。然而，测量全球日冕磁场仍然具有挑战性。日冕射电辐射的偏振特性对日冕磁场敏感。虽然它们可以被证明是日冕和日光层磁场的有用探测器，但它们的使用受到技术和算法挑战的限制。我们提出了一个强大的算法，精确的偏振校准和成像的低射频太阳观测，并证明它的数据从默奇森宽场阵列，平方公里阵列（SKA）的前身。该算法基于测量方程框架，该框架构成了所有现代无线电干涉校准和成像的基础。它提供了高动态范围和保真度的全斯托克斯太阳射电图像与仪器偏振泄漏$<1\%$，与一般的天文射电成像，并代表了国家的最先进的。开放这个有益的，但尚未探索，相空间将使多个新的科学调查，并提供相当大的发现潜力。例子包括探测来自热日冕发射的低水平圆偏振，以估计大规模的静止日冕场;探测来自日冕物质抛射的微弱回旋同步辐射的偏振，以可靠地估计等离子体参数;以及探测这些频率下的首次线性偏振。这种方法是在考虑SKA的情况下开发的，它将开启一个在低射频下进行高保真分光偏振快照太阳成像的新时代。
英文摘要：
Coronal magnetic fields are well known to be one of the crucial parameters defining coronal physics and space weather. However, measuring the global coronal magnetic fields remains challenging. The polarization properties of coronal radio emissions are sensitive to coronal magnetic fields. While they can prove to be useful probes of coronal and heliospheric magnetic fields, their usage has been limited by technical and algorithmic challenges. We present a robust algorithm for precise polarization calibration and imaging of low-radio frequency solar observations and demonstrate it on data from the Murchison Widefield Array, a Square Kilometer Array (SKA) precursor. This algorithm is based on the Measurement Equation framework, which forms the basis of all modern radio interferometric calibration and imaging. It delivers high dynamic range and fidelity full Stokes solar radio images with instrumental polarization leakages $<1\%$, on par with general astronomical radio imaging, and represents the state-of-the-art. Opening up this rewarding, yet unexplored, phase space will enable multiple novel science investigations and offer considerable discovery potential. Examples include detection of low-level of circularly polarization from thermal coronal emission to estimate large-scale quiescent coronal fields; polarization of faint gyrosynchrotron emissions from coronal mass ejections for robust estimation of plasma parameters; and detection of the first-ever linear polarization at these frequencies. This method has been developed with the SKA in mind and will enable a new era of high fidelity spectro-polarimetric snapshot solar imaging at low-radio frequencies.
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