太阳耀斑爆发微波频谱(20-40GHz)的相干测量与观测研究

A vast amount of energetic electrons is generated during a solar flare within a short interval of seconds to minutes. One most critical issue in solar flare studies is to figure out how so many electrons energized within such a short period. The gyro-synchrotron radiation emitted by energetic electrons moving in strong coronal magnetic fields is the main mechanism accounting for flare microwave bursts. The measurement of the flare microwave spectra and their temporal evolution provides important clues to understand the energy release and electron acceleration process and to diagnose critical parameters such as the magnetic field strength in the corona. Most previous instruments designed to measure the microwave spectra work under 20 GHz, and only few of them work at higher frequencies (such as 20-40 GHz). This leads to an incomplete measurement of the microwave spectra and makes it difficult to tell the accurate shape of the spectra. In this proposal we suggest to develop the observational system working in the microwave regime of 20-40 GHz. Starting from three bands centering around typical frequencies of 24, 30, 36 GHz, we aim to develop the key technologies of a two-element interferometer to measure the emission intensity (of the left and right handed circular polarizations). The technologies can greatly enhance the capability of removing radio interference from the background environment and from the quiet sun. Therefore, the sensitivity of the system can be greatly improved, in comparison with a traditional single-antenna radiometer. The calibrated data recorded by the system will be used for further analysis of the microwave spectra of solar flares within the frequency range of interest, so as to improve our understanding of the solar flare microwave spectra and the radio-emitting energetic electrons. In addition, this project will build the technology basis for further development of the observational system covering more frequencies and/or with the imaging capability.

耀斑过程可在秒至分钟尺度内加速产生大量高能电子。众多电子如何在短时内获取如此高能量是耀斑物理研究的核心问题。高能电子在磁化日冕中运动所激发的回旋同步辐射是耀斑微波爆发的主要辐射机制。耀斑微波辐射功率谱及其演化测量为认知耀斑能量释放和电子加速过程及日冕磁场等关键参数诊断提供了关键数据。以往国内外所发展的测量系统大都工作在<20GHz频段，在更高频段(如20-40GHz)仅有少数频点的测量。这导致现有数据难以精确判断微波频谱的完整谱形特征。本项目提议发展20-40GHz耀斑微波辐射观测系统，在选定的三个典型频带(~24, 30, 36GHz)发展二元天线相干测量关键技术及对应观测系统以有效提高耀斑微波观测的抗干扰能力和灵敏度。基于所获取的微波谱科学数据，我们将开展事件研究，提高对该频域耀斑微波谱和对应高能电子的理解；本项目还可为将来发展覆盖宽频系统和微波成像系统打下技术基础。

耀斑期间的微波辐射动态频谱及其演化特征是耀斑能量释放、粒子加速及磁场诊断重要的认知数据来源。但由于高频射电数据的匮乏，太阳爆发的物理研究亟需20-40 GHz频段的微波辐射数据。基于如上需求，在本项目中我们提出针对微波设备进行研发，并在关键技术突破、设备研制和常规观测及射电数据物理解读等方面取得系列成果：.1)掌握射电设备仪器关键技术，完成了频谱系统及相干系统研制。在天馈系统（宽带高增益天线设计、波束合成）、接收机系统（增益平坦度补偿、数字信号截位）、观测数据识别（爆发类型及尖峰暴自动识别、自适应观测）等方面取得技术突破，完成了35-40 GHz微波频谱系统、39.5-40 GHz相干系统研制，该系统可推广至20-40 GHz的宽带频域；.2)开展常规观测。目前已经针对35-40GHz太阳射电观测系统进行了一年半以上的常规观测，积累了大量的数据（经过压缩后1分钟约1GB数据），同时也结合国内外的相应爆发事件积极寻找对应事件；.3)项目组利用射电数据开展了相关工作。利用射电成像数据结合AIA的高分辨率EUV观测，分析了多支II型暴与耀斑-CME过程驱动激波的关系，并分别确定其源区位置；利用射电频谱结合多波段数据，发现在所研究事件中，HXR存在硬化特征，且随时间变得越来越显著，支持硬化能谱来自同源高能电子辐射产生的解释..项目执行期间，共发表 SCI 标注论文16篇，其中第一标注4篇，第二标注4篇，第三标注2篇，其它标注6 篇，申请并被授权国家发明专利6项。共有13篇论文发表于专业主流期刊Solar physics、APJS、ApJ等期刊之中。