arXivDaily arXiv每日学术速递 周一至周五更新
arXiv周末暂无论文更新,休息一下吧,周末愉快~~
arXiv 2407.19962astro-ph.HE
收藏

伽马射线暴余辉偏振的大尺度磁场模型:场各向异性、离轴视角与有序场的影响

Large-scale Magnetic Field Model of GRB Afterglow Polarization: Effects of Field Anisotropy, Off-axis Viewing Angle, and Ordered Field

Asuka Kuwata, Kenji Toma, Sara Tomita, Jiro Shimoda

AI总结:

本研究利用大尺度湍流同步辐射偏振半解析模型,探讨了磁场各向异性、观测者视角及有序场分量对伽马射线暴余辉偏振的影响,发现该模型能解释现有前向激波偏振观测数据,并指出恒定偏振需极高有序场能量占比但会导致偏振度过高。

摘要:

伽马射线暴的余辉是来自相对论性激波的非热电子同步辐射。辐射区强磁场的起源仍然难以捉摸,目前讨论了通过等离子体动力学和磁流体动力学不稳定性产生的两种磁场放大机制。偏振观测是区分这两种机制的有力探针。迄今为止,大多数理论研究集中于前一种机制,并构建了具有微观尺度湍流的余辉偏振模型,其相干长度远小于激波厚度。在本研究中,我们聚焦于后一种机制,利用我们的大尺度湍流同步辐射偏振半解析模型(其相干长度与激波厚度相当),研究磁场各向异性和观测者视角的影响。我们发现,大尺度湍流模型中的偏振既可表现出微观尺度湍流模型的典型行为,也能展现出微观尺度模型中未见的行为。随后我们发现,大尺度模型能够解释迄今为止所有看似前向激波辐射的偏振观测数据。我们还考察了有序场分量的影响,发现仅当有序与扰动分量的能量密度比 $\gtrsim 50$ 时,才能实现不随时间变化的偏振度和偏振角。然而在这种情况下,偏振度远高于观测值。

英文摘要:

The afterglows of gamma-ray bursts are non-thermal electron synchrotron emissions from relativistic shocks. The origin of strong magnetic field in the emission region remains elusive, and two field amplification mechanisms via the plasma kinetic and magnetohydrodynamic instabilities have been discussed. The polarimetric observations are a powerful probe to distinguish these two mechanisms. So far, most theoretical works have focused on the former mechanism and constructed afterglow polarization models with microscopic-scale turbulence whose coherence length is much smaller than the thickness of the blast wave. In this work, focusing on the latter mechanism, we utilize our semi-analytic model of the synchrotron polarization with large-scale turbulence whose coherence length is comparable to the thickness of the blast wave to investigate the effect of magnetic field anisotropy and the observer viewing angle. We find that the polarization in our large-scale turbulence model can exhibit both behaviors characteristic of the microscopic-scale turbulence model and those not seen in the microscopic-scale model. Then we find that the large-scale model could explain all the polarimetric observational data to date that seem to be forward shock emission. We also examine the effect of ordered-field component, and find that polarization degree and polarization angle constant in time are realized only when the energy density ratio of the ordered and fluctuated components is $\gtrsim 50$. In this case, however, the polarization degree is much higher than the observed values.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑