Afterglow Polarizations in a Stratified Medium with Effect of the Equal Arrival Time Surface
Afterglow Polarizations in a Stratified Medium with Effect of the Equal Arrival Time Surface
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DOI：
10.3847/1538-4357/acd6ef
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发表时间：
2023-05
期刊：
影响因子：
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通讯作者：
M. Lan;Xuefeng Wu;Z. Dai
中科院分区：
文献类型：
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作者：
M. Lan;Xuefeng Wu;Z. Dai
γ射线爆发的环境对射流动力学及其余辉的演化有重要影响。本文研究了具有等到达时间表面效应的层状介质中余辉的极化现象。预测了多波段余辉的极化。研究了分层介质参数对余辉偏振的影响。我们发现，在离轴探测中，余辉偏振度的变化对光阑效应的影响是非常重要的，偏振度的起伏随光阑效应的变化而向后移。即使磁场结构、喷流结构和观测角度是固定的，喷流发射的极化特性仍可能发生变化。在这里，我们假设反向激波区有一个大尺度有序磁场，正向激波区有一个二维随机场。因此，PD的演化主要由早期f32参数（逆激波区与正激波区之间的通量比）的演化和后期体洛伦兹因子γ的演化决定。通过对f32或γ的影响，观测能带、观测角度和分层介质参数最终会影响余辉偏振。
The environment of a γ-ray burst has an important influence on the evolution of jet dynamics and its afterglow. Here we investigate the afterglow polarizations in a stratified medium with the equal arrival time surface (EATS) effect. Polarizations of multiband afterglows are predicted. The effects of the parameters of the stratified medium on the afterglow polarizations are also investigated. We found the influences of the EATS effect on the afterglow polarizations become important for off-axis detections and polarization degree (PD) bumps move to later times with the EATS effect. Even if the magnetic field configurations, jet structure, and observational angles are fixed, polarization properties of the jet emission could still evolve. Here, we assume a large-scale ordered magnetic field in the reverse-shock region and a two-dimensional random field in the forward-shock region. Then, PD evolution is mainly determined by the evolution of the f 32 parameter (the flux ratio between the reverse-shock region and forward-shock region) at the early stage and by the evolution of the bulk Lorentz factor γ at the late stage. Through the influences on the f 32 or γ, the observational energy band, observational angles, and the parameters of the stratified medium will finally affect the afterglow polarizations.