双中子星并合中的多极中微子辐射：角结构、旋转变异性及对电子丰度的启示
Multipolar Neutrino Radiation in Binary Neutron Star Mergers: Angular Structure, Rotational Variability, and Implications for Electron Fraction
浏览论文内容
中文总结 AI 辅助
本研究通过广义相对论模拟结合M1中微子输运，揭示双中子星并合的中微子辐射具四极主导轴对称结构与0.6-0.7 kHz的m=1模式调制，且该结构诱导纬度相关的平衡电子丰度。
中文摘要 AI 辅助
通过完全广义相对论模拟，结合能量积分的M1中微子输运，在一组代表性的物态方程、总质量及质量比范围内，表征双中子星并合产生的中微子发射的角结构与时间变异性。在并合遗迹外的球面上提取与角度相关的中微子能流，并将其分解为球谐函数，以量化其多极成分与演化。初始并合后瞬变阶段结束后，中微子辐射流趋近于轴对称构型，由强四极分量主导，因环面遮挡产生持续的极向通量增强与赤道通量抑制；偶极贡献仍处于次主导地位，表明不存在持续的单侧发射。各向异性程度随质量不对称性增大及物态方程变软而增加，反映了遗迹-盘系统的致密性与形态。在该时间平均几何之上，识别出与m=1模式相关的相干方位角调制；傅里叶分析显示其特征频率约为0.6-0.7 kHz，与遗迹及内盘层的较差自转一致，表明旋转结构与中微子发射变异性存在动力学耦合。最后，量化了四极主导的辐射几何如何诱导出与纬度相关的平衡电子丰度：极向物质被驱动至接近中微子平衡目标，而赤道物质则系统性地更富含中子且低于平衡值。
英文摘要
The angular structure and temporal variability of neutrino emission from binary neutron star mergers are characterized using fully general-relativistic simulations with energy-integrated M1 neutrino transport across a representative set of equations of state, total masses, and mass ratios. The angle-dependent neutrino energy flux is extracted on a spherical surface outside the remnant and decomposed into spherical harmonics to quantify its multipolar content and evolution. Following the initial post-merger transient, the neutrino radiation flux approaches an axisymmetric configuration dominated by a strong quadrupolar component, producing persistent polar flux enhancement and equatorial suppression due to torus shadowing. The dipolar contribution remains subdominant, indicating the absence of sustained one-sided emission. The degree of anisotropy increases with mass asymmetry and for softer equations of state, reflecting the compactness and morphology of the remnant--disk system. Superimposed on this time-averaged geometry, coherent azimuthal modulations associated with the $m=1$ mode are identified. Fourier analysis reveals a characteristic frequency of $\sim 0.6$--$0.7$ kHz, consistent with differential rotation in the remnant and inner disk layers, indicating a dynamical coupling between rotational structure and neutrino emission variability. Finally, we quantify how the same quadrupole-dominated radiation geometry induces a latitude-dependent equilibrium electron fraction. The polar material is driven close to the neutrino-equilibrium target, whereas equatorial material remains systematically more neutron-rich and below equilibrium.
