We develop a model for the radio afterglow of the giant flare of SGR 1806-20 arising due to the interaction of magnetically dominated cloud, an analogue of Solar Coronal Mass Ejections (CMEs), with the interstellar medium (ISM). The CME is modelled as a spheromak-like configuration. The CME is first advected with the magnetar’s wind and later interacts with the ISM, creating a strong forward shock and complicated backwards exhaust flow. Using 3D magnetohydrodynamic simulations, we study various relative configurations of the magnetic field of the CME with respect to the ISM’s magnetic field. We show that the dynamics of the forward shock mostly follows the Sedov–Taylor blastwave, while the internal structure of the shocked medium is considerably modified by the back flow, creating a multiple shock configuration. We calculate synthetic synchrotron emissivity maps and light curves using two assumptions: (i) magnetic field compression; (ii) amplification of the magnetic field at the shock. We find that models with magnetic field amplification account better for the observed radio emission.

中文翻译：

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磁星巨大耀斑的无线电余辉

我们为 SGR 1806-20 巨大耀斑的射电余辉开发了一个模型，该模型是由于磁主导云（一种太阳日冕物质抛射 (CME) 的类似物）与星际介质 (ISM) 的相互作用而产生的。CME 被建模为类似 spheromak 的配置。CME 首先与磁星风平流，然后与 ISM 相互作用，产生强烈的前向冲击和复杂的向后排气流。使用 3D 磁流体动力学模拟，我们研究了 CME 磁场相对于 ISM 磁场的各种相对配置。我们表明，正向激波的动力学主要遵循 Sedov-Taylor 冲击波，而激波介质的内部结构被回流大大改变，形成了多重激波配置。我们使用两个假设计算合成同步辐射率图和光变曲线：（i）磁场压缩；(ii) 冲击时磁场的放大。我们发现具有磁场放大的模型更好地解释了观察到的无线电发射。