GRB 091208早期前激波余辉中观测到的10%极化的解释
Interpretations of the $10\%$ polarization observed in the early forward-shock afterglow of GRB 091208
中文总结 AI 辅助
本文针对GRB 091208早期前激波余辉观测到的10%极化高于传统预测的问题，通过同步辐射模型拟合观测数据，发现略微偏离轴线观测或存在大尺度有序磁场分量两种情景均可解释该结果。
中文摘要 AI 辅助
GRB 091208B早期阶段观测到的约10%的光学极化来自前激波辐射，该值高于传统预测值。前激波辐射的极化取决于观测几何和激波后磁场结构，这种磁场要么源于原有磁场（即外部介质中的磁场）的压缩，要么源于激波产生的不稳定性。本文使用同步辐射模型拟合GRB 091208B的光变曲线和极化观测结果，考虑两种情景：一是观测者略微偏离轴线，二是暴环境中存在大尺度有序磁场分量。研究发现两种情景均可解释GRB 091208B的观测结果：对于略微偏离轴线的观测情景，观测角被限制在喷流半张角的1.02至1.05倍范围内；对于大尺度有序磁场分量情景，有序分量与随机分量的比值被约束在1附近。
英文摘要
The $\sim10\%$ optical polarization observed at the early stage of GRB 091208B comes from the forward shock emission, which is higher than the conventionally predicted value. Polarizations of the forward shock radiation would depend on the observational geometry and the post-shock magnetic field structure. This magnetic field could arise either from the compression of a pre-existing magnetic field (i.e., the magnetic field in the outer medium) or from the shock-generated instabilities. In this paper, we use a synchrotron radiation model to fit the light curve and polarization observations of GRB 091208B. Two scenarios are considered: one is the case of a slightly off-axis observer, and the other is with a large-scale ordered magnetic field component in the burst environment. We found both scenarios could interpret the observations of GRB 091208B. For the slightly off-axis observation scenario, the observational angle is restricted to be within the range of (1.02, 1.05) times the jet half-opening angle. For the large-scale ordered magnetic field component scenario, the ratio between the ordered component to the random component is constrained to be around 1.
