Polarisation measurements of solar flares at millimetre-waves were used to investigate the magnetic field configuration of the emitting sources. We analyse two solar flares (SOL2013-02-17 and SOL2013-11-05) observed by the POlarisation Emission of Millimetre Activity at the Sun (POEMAS) at 45 and 90 GHz, at microwaves from 1 – 15 GHz by the Radio Solar Telescope Network (RSTN), and at high frequencies (212 GHz) by the Solar Submillimetre Telescope (SST). Also, hard X-rays from these flares were simultaneously detected by the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI). The flux and polarisation radio spectra were fit using a model that simulates gyrosynchrotron emission in a spatially-varying 3D magnetic field loop structure. For the modelling, the magnetic loop geometry was fixed and the field strength was the only free parameter of the magnetic field. In addition, a uniform electron distribution was assumed by the model, with the number density of energetic electrons and the electron spectral index as free parameters. The fitted model reproduced reasonably well the observed degree of polarisation and radio flux spectra for each event yielding the physical parameters of the loop and flaring sources. Our results indicate that the high degree of polarisation during a solar flare can be explained by two sources located at the footpoints of highly asymmetric magnetic loops whereas low polarisation degrees arise from footpoint sources of symmetric magnetic loops.

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从毫米波偏振度推断太阳耀斑的磁场不对称性

毫米波太阳耀斑的偏振测量用于研究发射源的磁场配置。我们分析了两个太阳耀斑（SOL2013-02-17 和 SOL2013-11-05），由射电太阳望远镜在 45 GHz 和 90 GHz 频率下的太阳毫米波活动偏振发射 (POEMAS) 观测到的 1 – 15 GHz网络 (RSTN)，以及太阳能亚毫米望远镜 (SST) 的高频 (212 GHz)。此外，来自这些耀斑的硬 X 射线同时被鲁文拉马蒂高能太阳光谱成像仪 (RHESSI) 探测到。使用在空间变化的 3D 磁场回路结构中模拟陀螺同步加速器发射的模型来拟合通量和极化射电频谱。对于建模，磁环几何形状是固定的，场强是磁场的唯一自由参数。此外，模型假设电子分布均匀，高能电子数密度和电子谱指数作为自由参数。拟合模型相当好地再现了观测到的每个事件的极化程度和无线电通量谱，产生了环和耀斑源的物理参数。我们的结果表明，太阳耀斑期间的高度极化可以通过位于高度不对称磁环脚点的两个源来解释，而低极化度则来自对称磁环的脚点源。以高能电子数密度和电子谱指数为自由参数。拟合模型相当好地再现了观测到的每个事件的极化程度和无线电通量谱，产生了环和耀斑源的物理参数。我们的结果表明，太阳耀斑期间的高度极化可以用位于高度不对称磁环脚点的两个源来解释，而低极化度则来自对称磁环的脚点源。以高能电子数密度和电子谱指数为自由参数。拟合模型相当好地再现了观测到的每个事件的极化程度和无线电通量谱，产生了环和耀斑源的物理参数。我们的结果表明，太阳耀斑期间的高度极化可以用位于高度不对称磁环脚点的两个源来解释，而低极化度则来自对称磁环的脚点源。