Modeling the Thermal Low-Frequency Radio Sun with Ray Tracing
利用射线追踪建模热低频射电太阳
Peijin Zhang, Bin Chen, Gregory Fleishman, Alexey Kuznetsov, Cooper Downs, Surajit Mondal, Sijie Yu
AI总结 本文开发了一个结合射线追踪和辐射传输的前向建模框架,用于模拟日冕热等离子体在40–800 MHz频段的射电辐射,并验证了其对宁静太阳背景谱的再现能力。
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米波-分米波波段的非相干射电辐射提供了日冕热等离子体的关键诊断,但在低于~1 GHz的频率下,日冕折射会显著弯曲射线路径并改变视源大小和亮度分布。我们开发了一个前向建模框架,该框架将全局三维日冕模型中的折射射线追踪与沿每条射线的辐射传输相结合。该方法使用逐步扰动回溯方法追踪射线管横截面积$S(s)$,并引入与$d\ln S/ds$成正比的几何放大项,以在聚焦/散焦下强制执行通量守恒。然后使用 exttt{GRFF}辐射传输代码计算热自由-自由发射和吸收,生成40–800 MHz的合成射电图。将该框架应用于卡林顿自转2298,我们发现包含传播效应可以很好地再现宁静太阳背景谱。然而,活动区亮度的建模精度较低,表明未来工作中应考虑额外的物理因素。这些结果建立了一种基于物理的方法,用于生成低频宁静太阳合成图像,适用于与干涉观测进行定量比较,并评估传播效应如何塑造观测形态。
Incoherent radio emission at meter--decimeter wavelengths provides a key diagnostic of the coronal thermal plasma, but at frequencies below $\sim$\,1\,GHz coronal refraction can substantially bend ray paths and modify the apparent source size and brightness distribution. We develop a forward-modeling framework that combines refractive ray tracing through a global 3D coronal model with radiative transfer along each ray. The method tracks the ray-tube cross-sectional area $S(s)$ using a step-wise perturbation retracing approach and incorporates a geometric magnification term proportional to $d\ln S/ds$ to enforce flux conservation under focusing/defocusing. Thermal free--free emission and absorption are then computed with the \texttt{GRFF} radiative transfer code to produce synthetic radio maps over 40--800\,MHz. Applying the framework to Carrington rotation 2298, we find that including propagation effects allows the quiet-Sun background spectrum to be well reproduced. However, active region brightness is less accurately modeled, suggesting that additional physical factors should be considered in future work. These results establish a physics-based method for generating low-frequency quiet-Sun synthetic images suitable for quantitative comparison with interferometric observations and for assessing how propagation effects shape the observed morphology.