在重复快速射电暴中探测到90%的圆偏振
Ninety percent circular polarization detected in a repeating fast radio burst
AI总结：
本研究在重复快速射电暴FRB 20201124A中探测到90.9±1.1%的极高圆偏振度，还发现线偏振位置角的快速摆动与正交跳变，为快速射电暴的物理机制提供了强约束。
摘要：
快速射电暴（FRBs）是物理机制未知的河外射电源。它们会持续数毫秒的射电脉冲，其各向同性等效能量为$10^{36}\sim10^{41}$ erg。这对应的快速射电暴辐射亮温度通常可达$10^{36}$ K量级，但在亚微秒时标的结构中可高达$10^{40}$ K以上，表明其背后存在相干相对论性辐射机制。偏振是理解快速射电暴物理起源的关键信息：线偏振通常可示踪磁场的几何构型，而圆偏振则可探测内禀辐射机制与传播效应。本文研究显示，重复暴源FRB 20201124A会辐射出圆偏振度达$90.9\pm1.1\\\\%$的射电脉冲。如此高的圆偏振度在理论上未曾被预料到，在快速射电暴观测中也属史无前例——此前这类高圆偏振度仅在太阳或木星的射电活动中常见，被归因于亚相对论电子的作用。我们注意到，圆偏振度与暴的注量之间不存在明显相关性。除了高圆偏振度之外，我们还探测到线偏振位置角的快速摆动和正交跳变。FRB 20201124A中高圆偏振度的探测，结合其呈现正交模式的线偏振特性，对快速射电暴的物理机制构成了强约束，表明磁层辐射与传播效应的共同作用塑造了观测到的快速射电暴辐射。
英文摘要：
Fast radio bursts (FRBs) are extra-galactic sources with unknown physical mechanisms. They emit millisecond-duration radio pulses with isotropic equivalent energy of $10^{36}\sim10^{41}$ ergs. This corresponds to a brightness temperature of FRB emission typically reaching the level of $10^{36}$ K, but can be as high as above $10^{40}$ K for sub-microsecond timescale structures, suggesting the presence of underlying coherent relativistic radiation mechanisms. Polarization carries the key information to understand the physical origin of FRBs, with linear polarization usually tracing the geometric configuration of magnetic fields and circular polarization probing both intrinsic radiation mechanisms and propagation effects. Here we show that the repeating sources FRB 20201124A emits $90.9\pm 1.1\%$ circularly polarized radio pulses. Such a high degree of circular polarization was unexpected in theory and unprecedented in observation in the case of FRBs, since such a high degree of circular polarization was only common among Solar or Jovian radio activities, attributed to the sub-relativistic electrons. We note that there is no obvious correlation between the degree of circular polarization and burst fluence. Besides the high degree of circular polarization, we also detected rapid swing and orthogonal jump in the position angle of linear polarization. The detection of the high degree circular polarization in FRB 20201124A, together with its linear polarization properties that show orthogonal modes, place strong constraints on FRB physical mechanisms, calling for an interplay between magnetospheric radiation and propagation effects in shaping the observed FRB radiation.
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