Photospheric Polarization Signatures from Long Gamma-Ray Burst Simulations
Photospheric Polarization Signatures from Long Gamma-Ray Burst Simulations
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DOI：
10.3847/1538-4357/ab910f
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发表时间：
2020-05
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影响因子：
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通讯作者：
T. Parsotan;D. López-Cámara;D. Lazzati
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文献类型：
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作者：
T. Parsotan;D. López-Cámara;D. Lazzati
由于围绕在这些事件中起作用的辐射机制的各种问题，对伽马射线暴（GRBs）的全面理解一直难以捉摸。伽玛暴的偏振测量可以在很大程度上约束伽玛暴喷流的相关辐射机制和结构；然而，可以与观测到的GRB极化进行比较的理论预测数量有限。本文利用蒙特卡洛辐射输运（MCRaT）代码对一组二维相对论流体力学长伽马射线暴（LGRB）射流模拟进行了辐射传输计算，包括恒定射流和可变射流。极化的加入增强了MCRaT；首先通过再现文献中的各种结果对其进行验证，然后用于获得合成lgrb的时间积分和时间分辨偏振度和角度。虽然得到的时间积分极化度（> 1%）与POLAR实验的约束条件一致，但由于我们使用的模型射流剖面中缺乏强梯度，它们低于其他理论研究结果。时间分辨结果表明，在光曲线最亮的部分，具有宽喷流的grb具有较小的偏振度（小于2%）和恒定的偏振角。离轴观测到的伽马射线暴偏振度和偏振角会随着流出体辐射壳的时间结构而变化。然后，我们将我们的结果放在GRB提示发射模型以及未来LEAP和POLAR-2 GRB偏振测量的背景下。
A comprehensive understanding of gamma-ray bursts (GRBs) has been elusive due to the variety of questions surrounding the radiation mechanism at play in these events. Polarization measurements of GRBs can heavily constrain the relevant radiation mechanisms and the structure of the GRB jet; however, there is a limited number of theoretical predictions that observed GRB polarizations can be compared against. Here, we conduct radiative transfer calculations of a set of two-dimensional relativistic hydrodynamic long GRB (LGRB) jet simulations, of a constant and a variable jet, using the Monte Carlo Radiation Transport (MCRaT) code. MCRaT has been enhanced by the inclusion of polarization; it has been first verified by reproducing a variety of results in the literature and then used to obtain the time-integrated and time-resolved polarization degrees and angles of the synthetic LGRBs. While the obtained time-integrated polarization degrees (≲1%) are consistent with the constraints from the POLAR experiment, they are lower than other theoretical studies due to the lack of strong gradients in the model jet profiles that we use. The time-resolved results suggests that GRBs with wide jets observed on axis will have small polarization degrees (≲2%) and constant polarization angles, during the brightest portion of the light curve. GRBs observed off-axis will have larger polarization degrees and polarization angles that change with the temporal structure of radiating shells in the outflow. We then place our results in the context of GRB prompt emission models and future LEAP and POLAR-2 GRB polarimetry detections.