双中子星并合抛射物秒级演化的三维研究：动力学、元素分布与光变曲线
3D Binary Neutron Star Merger Ejecta Evolution up to Seconds Timescale: Dynamics, Element Distribution, and Light Curves
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中文总结 AI 辅助
通过对4个双中子星并合抛射物开展秒级三维数值模拟，结合核加热与多视角光变曲线计算，发现提高维度难以让理论模型匹配AT2017gfo观测结果。
中文摘要 AI 辅助
我们对4个双中子星并合产生的抛射物开展了长达秒级的三维数值模拟。数值相对论数据作为边界条件，用于广义相对论流体动力学演化，该演化过程采用了核统计平衡之外适用的物态方程，以及基于反应网络计算的有效核加热方案。我们研究了抛射物的动力学与几何特性、核加热的影响、元素的形成与空间分布，并计算了多视角千新星光变曲线。核加热显著影响抛射物动力学，延迟了秒级之外的同源膨胀，并重塑了重核的空间分布。对于具有长寿命遗迹的非对称双中子星，该效应最为显著；将演化时间从~150毫秒延长至~1秒，包含90%重元素质量（如Z=56、Z=79）的极角区域范围从|θ|≲15°扩大至|θ|≲30°。我们的核合成结果证实，56Ni→56Co→56Fe衰变链在~100天主导加热，钴衰变产生846.77和1238.288keV的伽马射线线。对比从多视角三维轮廓获得的千新星逐射线光变曲线与平均二维轮廓的结果，发现后者方法大体可靠，但二维光变曲线应视为上限。提高维度通常会降低热光度，且双中子星的非对称性增强了视角依赖性。对于与镧系物质幕最密区域对齐的观测者，三维发射的亮度可与对应二维结果匹配。我们得出结论：仅提高维度不太可能使当前理论模型与AT2017gfo观测结果吻合。
英文摘要
We present long-term, three-dimensional simulations of ejecta from four binary neutron star mergers to second-long time-scales. Numerical-relativity data serve as boundary conditions for a general-relativistic hydrodynamics evolution incorporating an equation of state valid outside nuclear statistical equilibrium and an effective nuclear-heating prescription based on reaction-network calculations. We investigate the ejecta's dynamical and geometrical properties, the impact of nuclear heating, the formation and spatial distribution of elements, and compute multi-angle kilonova light curves. % Nuclear heating significantly affects ejecta dynamics, delaying homologous expansion beyond second time-scales and reshapes the spatial distribution of heavy nuclei. This effect is largest for asymmetric binaries with long-lived remnants; extending the evolution from ${\sim}150$~ms to ${\sim}1$~s widens the angular polar region containing 90\% of the heavy-element mass (\eg, $Z=56$, $Z=79$) from $|θ|\lesssim15^{o}$ to $|θ|\lesssim30^{o}$. Our nucleosynthesis results confirm that the $^{56}$Ni$\rightarrow^{56}$Co$\rightarrow^{56}$Fe decay chain dominates the heating at $\sim$100 days, with cobalt decay producing gamma-ray lines at 846.77 and 1238.288~keV. % Comparing kilonova ray-by-ray light curves obtained from multi-angle 3D profiles and averaged 2D profiles, we find the latter approach broadly robust, although 2D light curves should be treated as upper limits. Increasing dimensionality generally lowers the bolometric luminosity, with binary asymmetry strengthening the viewing-angle dependence. For observers aligned with a lanthanide curtain's densest region, 3D emission can match its 2D counterpart in brightness. We conclude that increased dimensionality alone is unlikely to reconcile current theoretical models with AT2017gfo observations.
