SALT/SAAO观测和AT 2017 gfo的kilonova模型之间的比较：引力波瞬变的第一个电磁对应物- GW170817
A comparison between SALT/SAAO observations and kilonova models for AT 2017gfo: the first electromagnetic counterpart of a gravitational wave transient - GW170817
摘要：
我们报告了在发现的前10天内，在NGC 4993星系中的kilonova AT 2017 gfo（又名SSS 17 a）的其他SAAO望远镜（MASTER SAAO和IRSF）进行的SALT低分辨率光谱学和光学/红外测光。这一事件已被确定为有史以来第一个电磁对应的引力波事件，即GW 170817，这是由LIGO和Virgo引力波天文台检测到的。这一事件很可能是由于两颗中子星的合并，导致了千诺瓦爆炸。SALT是第三台获得AT 2017 gfo光谱的望远镜，第一个光谱，合并后1.2 d，是相当蓝色的，显示出一些广泛的特征，但没有可识别的谱线，并随着时间的推移变得更红。我们比较光谱和光度的演变与最近的kilonova模拟，并得出结论，他们是在定性协议合并后的风模型与质子：核子比$Y_e$ = 0.25 $-$ 0.30。第一个光谱的蓝色与喷出物中不含镧系元素的r过程元素的较低不透明度一致。模型和观测结果之间的差异可能是由于系统参数的选择，以及喷出物模型中缺乏更多元素的原子数据。
英文摘要：
We report on SALT low resolution optical spectroscopy and optical/IR photometry undertaken with other SAAO telescopes (MASTER-SAAO and IRSF) of the kilonova AT 2017gfo (aka SSS17a) in the galaxy NGC4993 during the first 10 days of discovery. This event has been identified as the first ever electromagnetic counterpart of a gravitational wave event, namely GW170817, which was detected by the LIGO and Virgo gravitational wave observatories. The event is likely due to a merger of two neutron stars, resulting in a kilonova explosion. SALT was the third telescope to obtain spectroscopy of AT 2017gfo and the first spectrum, 1.2 d after the merger, is quite blue and shows some broad features, but no identifiable spectral lines and becomes redder over time. We compare the spectral and photometric evolution with recent kilonova simulations and conclude that they are in qualitative agreement for post-merger wind models with proton: nucleon ratios of $Y_e$ = 0.25$-$0.30. The blue colour of the first spectrum is consistent with the lower opacity of the Lathanide-free r-process elements in the ejecta. Differences between the models and observations are likely due to the choice of system parameters combined with the absence of atomic data for more elements in the ejecta models.
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