伽马射线暴瞬时阶段的偏振角旋转——II. 参数的影响
Rotation of Polarization Angle in Gamma-Ray Burst Prompt Phase$-$\uppercase\expandafter{\romannumeral2}. The Influence of The Parameters
AI总结：
本研究基于带大尺度有序磁场的磁重联模型，探究伽马射线暴瞬时阶段偏振角旋转的参数影响规律，发现其由喷流半张角与洛伦兹归一化因子的乘积主导，并给出了不同参数下的偏振角变化范围与极端旋转条件。
摘要：
除光变曲线和能谱外，偏振也是推断伽马射线暴（Gamma-ray burst，GRB）物理性质的重要依据。偏振角（polarization angle，PA）随时间的旋转会导致时间积分偏振度出现退偏效应，但该现象此前鲜有研究。本文采用辐射区存在大尺度有序排列磁场的磁重联模型，研究GRB瞬时阶段各参数对PA旋转的影响。研究发现，喷流半张角$θ_{j}$、观测角$θ_{V}$以及体洛伦兹因子$Γ$均对PA旋转有显著影响。PA旋转受$θ_{j}Γ_{0}$的乘积值调控（其中$Γ_{0}$是$Γ$的归一化因子，满足$Γ(r)=Γ_{0}(r/r_{0})^{s}$），但与$θ_{j}$和$Γ_{0}$各自的具体取值大致无关。对于典型参数，在轻微离轴观测情形下，$T_{90}$（即累积流量密度从5%到95%对应的暴持续时间）内的PA变化量（$\triangle$PA）处于$(12^\bullet, 66^\bullet)$区间内。随着$θ_{j}Γ_{0}$乘积值增大，满足$\triangle$PA$>10^{\bullet}$的$q$取值范围会缩小。当$θ_{j}Γ_{0}>50$且$1.0<q≤1.2$时，会出现$\triangle$PA约为$90^{\bullet}$的最显著PA旋转。
英文摘要：
In addition to the light curve and energy spectrum, polarization is also important for inferring the physical properties of the Gamma-ray burst (GRB). Rotation of the polarization angle (PA) with time will cause depolarization of the time-integrated polarization degree. However, it is rarely studied before. Here, we use a magnetic reconnection model with a large-scale ordered aligned magnetic field in the emitting region to study the influence of the parameters on the PA rotations in GRB prompt phase. We find that half-opening angle of the jet $θ_{j}$, the observational angle $θ_{V}$, and the bulk Lorentz factor $Γ$ all have significant impacts on the PA rotations. The PA rotations are affected by the product value of $θ_{j}Γ_{0}$ ($Γ_{0}$ is the normalization factor of $Γ$ with $Γ(r)=Γ_{0}(r/r_{0})^{s}$), but are roughly independent of the concrete values of both $θ_{j}$ and $Γ_{0}$. For the typical parameters, the changes of the PA within $T_{90}$ ($\triangle$PA) would be within ($12^\circ$, $66^\circ$) for slight off-axis observations, where $T_{90}$ is the duration of the burst with the accumulated flux density ranging from $5\%$ to $95\%$. The $q$ range for $\triangle$PA$>10^{\circ}$ becomes smaller with the increase of the product value of $θ_{j}Γ_{0}$. The most significant PA rotation with $\triangle$PA$\sim90^{\circ}$ will happen when $θ_{j}Γ_{0}>50$ and $1.0<q\leq1.2$.
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。
