Late-time emission-line profiles from kilonova models
千新星模型晚期的发射线轮廓
Numerical simulations suggest that neutron star mergers eject material with complex, non-spherical density and composition distributions. Here we use two-dimensional configurations of merger ejecta obtained from long-term hydrodynamic simulations to quantify the influence of such ejecta structure on the shapes of spectral lines in the optically thin limit. We consider three example elements of interest for kilonova modelling (selenium, tellurium and tungsten) and illustrate profile shapes for a sample of models and observer orientations. Many of our calculations yield complex profile shapes, including cases with multiple peaks and/or extended wings on scales large enough to be relevant to interpreting observations. For selenium and tellurium, our late-phase profile shapes are most sensitive to the structure of the low-velocity ejecta (~0.1c) launched after the merger from the relic black-hole torus system, while for heavier elements the contribution from the more rapidly expanding and more neutron-rich dynamical ejecta launched right after the merger is more significant and leads to broader line shapes. We also find that the dynamical influence of heating due to the decay of r-process elements can lead to considerably broader peaks than suggested by models that neglect this effect. Although idealised, our calculations demonstrate that line shapes are sensitive to the ejecta structure and could therefore constrain the polar observation angle or underlying properties of the merger that determine the spatial distributions of elements in the ejecta components, such as the binary mass ratio or even the equation of state of high-density matter.
展开 ▾首次基于长期动力学模拟的二维抛射物结构计算多种元素的线轮廓,发现线轮廓可呈现多峰、扩展翼等复杂形态,r-过程加热显著展宽线心,并指出这些特征可约束并合参数及观测倾角。
千新星早期光谱由于高光深呈现球对称特征 Sneppen+ 2023,但晚期光学薄时线轮廓可反映抛射物几何 Jerkstrand 2017。以往多数晚期发射线研究采用一维或高斯近似 Hotokezaka+ 2023,而本文基于二维并合模拟 Just+ 2023 首次系统探究了不同元素在不同方向的轮廓变化。未来需要在三维模型中考虑温度/电离梯度、谱线混叠和残余光深 Pognan+ 2023,有望通过线轮廓观测约束径向元素分层及并合参数如质量比和状态方程 Sneppen+ 2026。