标题： 伽马射线暴瞬时辐射中相对论热电子和非热电子混合分布的同步辐射偏振 显示英文标题

标题： Synchrotron polarization of a hybrid distribution of relativistic thermal and nonthermal electrons in GRB prompt emission

摘要： 伽马射线暴（GRBs）中相对论非热电子的同步自辐射偏振已被广泛研究。然而，最近关于相对论激波和磁重联的数值模拟发现，更现实的电子分布由幂律分量加上热分量组成，这需要观测验证。本文中，我们研究了在GRB瞬时辐射中全球环形磁场内相对论热电子和非热电子混合能谱的同步自辐射偏振。我们的结果显示，与仅有非热电子的情况相比，在这些混合电子中的同步自辐射偏振度（PDs）可以因不同参数而发生显著变化，并且PD随频率在$\gamma$射线、X射线和光学波段逐渐减小。时间平均PD谱在$\gamma$射线和X射线波段显示一个显著的峰值，PD高于$\sim60\%$，如果电子的热峰能量远小于热分布和非热分布之间的连接能量。在$\gamma$射线和X射线波段的高同步自辐射PD（$\gtrsim 60\%$），通常不能仅由具有典型幂律斜率的非热电子产生，但可以通过混合电子实现，主要来源于热分量的指数衰减部分。此外，该模型可以大致解释某些GRB的PDs和光谱特性，其中具有高PD（$70_{-22}^{+22} \%$）的GRB 110301A可能是相对论热电子存在的潜在证据。 显示英文摘要

摘要： Synchrotron polarization of relativistic nonthermal electrons in gamma-ray bursts (GRBs) has been widely studied. However, recent numerical simulations of relativistic shocks and magnetic reconnection have found that a more realistic electron distribution consists of a power-law component plus a thermal component, which requires observational validation. In this paper, we investigate synchrotron polarization using a hybrid energy distribution of relativistic thermal and nonthermal electrons within a globally toroidal magnetic field in GRB prompt emission. Our results show that, compared to the case of solely non-thermal electrons, the synchrotron polarization degrees (PDs) in these hybrid electrons can vary widely depending on different parameters and that the PD decreases progressively with frequency in the $\gamma$-ray, X-ray, and optical bands. The time-averaged PD spectrum displays a significant bump in the $\gamma$-ray and X-ray bands with the PDs higher than $\sim60\%$ if the thermal peak energy of electrons is much smaller than the conjunctive energy of electrons between the thermal and non-thermal distribution. The high synchrotron PD ($\gtrsim 60\%$) in the $\gamma$-ray and X-ray bands, which generally can not be produced by solely non-thermal electrons with typical power-law slopes, can be achieved by the hybrid electrons and primarily originates from the exponential decay part of the thermal component. Moreover, this model can roughly explain the PDs and spectral properties of some GRBs, where GRB 110301A with a high PD ($70_{-22}^{+22} \%$) may be potential evidence for the existence of relativistic thermal electrons.