Spectroscopic identification of r-process nucleosynthesis in a double neutron-star merger
Spectroscopic identification of r-process nucleosynthesis in a double neutron-star merger
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DOI：
10.1038/nature24298
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发表时间：
2017-10
期刊：
影响因子：
64.8
通讯作者：
E. Pian;P. D’Avanzo;S. Benetti;M. Branchesi;E. Brocato;S. Campana;E. Cappellaro;S. Covino;
中科院分区：
文献类型：
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作者：
E. Pian;P. D’Avanzo;S. Benetti;M. Branchesi;E. Brocato;S. Campana;E. Cappellaro;S. Covino;
据预测，两颗中子星的合并将产生三种主要的可探测现象：γ射线的短爆发，引力波信号，以及由大量重元素通过快速中子捕获（r过程）合成而产生的瞬态光学近红外源。这种被称为“macroovae”或“kilonovae”，，，，的瞬变被认为是黄金和铂等稀有元素的生产中心。到目前为止，关于千新星最令人信服的证据是在短γ射线爆发的余辉中出现了非常微弱的近红外再亮现象，红移系数为0.356，尽管已经有报道表明有更蓝的事件发生。在这里，我们报告了一颗与引力波源GW170817和γ射线暴GRB 170817A有关的明亮千新星的光谱识别和物理特性，GRB 170817A与距离地球40兆秒差距的星系有关。利用一系列来自地面观测站的光谱，覆盖了从紫外到近红外的波长范围，我们发现千新星的特征是快速膨胀的喷出物，其光谱特征与当前模型预测的相似。喷射物在早期具有光学厚度，速度约为光速的0.2倍，并在1.5天内达到约50个天文单位的半径。随着抛射物的膨胀，光谱连续体上出现了宽的吸收样线，表明在合并后快速移动的动态抛射物和两个较慢（0.05倍光速）的风区中发生的核合成产生的原子种类。与光谱模型的比较表明，这次合并喷射出了0.03到0.05个太阳质量的物质，包括高不透明度的镧系元素。
The merger of two neutron stars is predicted to give rise to three major detectable phenomena: a short burst of γ-rays, a gravitational-wave signal, and a transient optical–near-infrared source powered by the synthesis of large amounts of very heavy elements via rapid neutron capture (the r-process),,. Such transients, named ‘macronovae’ or ‘kilonovae’,,,, are believed to be centres of production of rare elements such as gold and platinum. The most compelling evidence so far for a kilonova was a very faint near-infrared rebrightening in the afterglow of a short γ-ray burst,at redshiftz= 0.356, although findings indicating bluer events have been reported. Here we report the spectral identification and describe the physical properties of a bright kilonova associated with the gravitational-wave source GW170817 and γ-ray burst,GRB 170817A associated with a galaxy at a distance of 40 megaparsecs from Earth. Using a series of spectra from ground-based observatories covering the wavelength range from the ultraviolet to the near-infrared, we find that the kilonova is characterized by rapidly expanding ejecta with spectral features similar to those predicted by current models,. The ejecta is optically thick early on, with a velocity of about 0.2 times light speed, and reaches a radius of about 50 astronomical units in only 1.5 days. As the ejecta expands, broad absorption-like lines appear on the spectral continuum, indicating atomic species produced by nucleosynthesis that occurs in the post-merger fast-moving dynamical ejecta and in two slower (0.05 times light speed) wind regions. Comparison with spectral models suggests that the merger ejected 0.03 to 0.05 solar masses of material, including high-opacity lanthanides.