Modelling the spectra of the kilonova AT2017gfo -- II: Beyond the photospheric epochs

Understand

Binary neutron star mergers are the first confirmed site of element nucleosynthesis by the rapid neutron-capture process (r-process).

• The kilonova AT2017gfo is the only electromagnetic counterpart of a neutron star merger spectroscopically observed.
• We analyse the entire spectral sequence of AT2017gfo (from merger to +10.4 days) and identify seven emission-like features.
• We confirm that the prominent 1.08 um feature can be explained by the Sr II near-infrared triplet evolving from a P-Cygni profile through to pure emission.