标题： 与γ射线暴相关的重元素核合成 显示英文标题

标题： Heavy element nucleosynthesis associated with a gamma-ray burst

摘要： 千 nova 是一类新型的天文学暂现源，也是目前宇宙中唯一被观测证实的快速中子俘获过程（r 过程）发生地。 迄今为止，仅有少数几个千 nova 被探测到，其中只有一个光谱上被确认的事件（AT 2017gfo）。AT 2017gfo 的光谱提供了比铁更重元素形成的证据；然而，这些光谱是在最初约 10 天内收集的，此时轻 r 过程元素的辐射主导了观测。 如果合成出了更重的元素，它们预计将影响千 nova 晚期演化的阶段，而这些阶段超出了我们已有光谱观测的范围。 在这里，我们报告了一个快速变红的热暂现源的光谱观测，该暂现源紧随伽马射线暴 GRB 230307A 之后。 早期（2.4 天）光学光谱识别出一个高温（T ~ 6700 K）热连续谱的存在。 到第 29 天时，这一成分显著扩展和冷却（T ~ 640 K），但仍保持光学厚，表明存在高消光系数的喷发物质。 我们展示出这些性质只能通过致密天体的合并来解释，并进一步推断出重镧系元素的产生。 我们识别出几个光谱特征（在吸收和发射中），其成因可以通过新合成的重元素来解释。 这一事件标志着第二次记录到的 r 过程元素合成的光谱证据，也是首次在如此晚的阶段被观测到的。 显示英文摘要

摘要： Kilonovae are a novel class of astrophysical transients, and the only observationally-confirmed site of rapid neutron capture nucleosynthesis (the r-process) in the Universe. To date, only a handful of kilonovae have been detected, with just a single spectroscopically-observed event (AT 2017gfo). Spectra of AT 2017gfo provided evidence for the formation of elements heavier than iron; however, these spectra were collected during the first ~ 10 days, when emission from light r-process elements dominates the observations. Heavier elements, if synthesised, are expected to shape the late-time evolution of the kilonova, beyond the phases for which we have spectral observations. Here we present spectroscopic observations of a rapidly-reddening thermal transient, following the gamma-ray burst, GRB 230307A. Early (2.4 day) optical spectroscopy identifies the presence of a hot (T ~ 6700 K) thermal continuum. By 29 days, this component has expanded and cooled significantly (T ~ 640 K), yet it remains optically thick, indicating the presence of high-opacity ejecta. We show that these properties can only be explained by the merger of compact objects, and further, leads us to infer the production of the heavy lanthanide elements. We identify several spectral features (in both absorption and emission), whose cause can be explained by newly-synthesised heavy elements. This event marks only the second recorded spectroscopic evidence for the synthesis of r-process elements, and the first to be observed at such late times.