The observed abrupt twice-90° rotations of the polarization angle (PA) in the prompt phase of gamma-ray bursts (GRBs) are difficult to understand within the current one-emitting-shell models. Here, we apply a model with multiple emitting shells to solve this new challenging problem. Two configurations of large-scale ordered magnetic fields in the shells are considered: toroidal and aligned. Together with the light curves and the spectral peak energy evolutions, the twice-90° PA rotations in GRB 170114A and GRB 160821A could be well interpreted with the multishell aligned magnetic field configuration (MFC). Our numerical calculations also show that the multiple shells with the toroidal MFC could not explain the observed twice-90° PA rotations. An aligned MFC in the GRB outflow usually indicates the preference of a magnetar central engine, while a toroidal field configuration is typically related to a central black hole. Therefore, the magnetar central engines for the two GRBs are favored.

中文翻译：

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GRB 170114A 和 GRB 160821A 中偏振角两次 90° 旋转的起源


在伽玛射线暴（GRB）的瞬发阶段观察到的偏振角（PA）突然旋转两次至 90°，在当前的单发射壳层模型中很难理解。在这里，我们应用具有多个发射壳的模型来解决这个新的具有挑战性的问题。考虑壳中大规模有序磁场的两种配置：环形和对齐。结合光变曲线和光谱峰值能量演化，GRB 170114A 和 GRB 160821A 中两次 90° PA 旋转可以通过多壳对齐磁场配置 (MFC) 得到很好的解释。我们的数值计算还表明，具有环形 MFC 的多壳无法解释观察到的两次 90° PA 旋转。 GRB 流出中对齐的 MFC 通常表明磁星中心引擎的偏好，而环形场配置通常与中心黑洞相关。因此，两颗伽玛暴的磁星中央发动机受到青睐。