A kilonova as the electromagnetic counterpart to a gravitational-wave source (Smartt+2017) The discovery of the first kilonova AT2017gfo. I carried out the light curve fitting to derive first estimates of ejecta mass and expansion velocities.
Hydrogen-rich supernovae beyond the neutrino-driven core-collapse paradigm (Terreran+2017) Discovery a a truly remarkable Type II SN that looks like a scaled-up version of a BSG explosion like SN 1987A, but emits 100 times more energy.
Multi-messenger Observations of a Binary Neutron Star Merger (Abbott+2017) The cross-consortium paper on the kilonova discovery, summarizing the view from all data from a global perspective.
Inelastic e+Mg collision data and its impact on modelling stellar and supernova spectra (Barklem+2017) Magnesium lines play a key role in the diagnosis of CCSN spectra. The Mg I] 4571 line is almost always strong, and helps us diagnose important ratios like Mg/O that are determined by convective processes as well as nuclear cross section. In fact, the solar Mg/O ratio has long been somewhat of a conundrum as stellar evolution models tend to produce too low values (see Arnett book for a good discussion of this). Here, new accurate collision strengths were calculated by the Uppsala atomic physics group, and the impact of these on SN modelling was tested with SUMO. As a reminder of a lesson we learn but keep forgetting, the models are only as good as the atomic data; here new cross section lead to up to a factor 2 different Mg I lines in SUMO.
Discovery of Molecular Hydrogen in SN 1987A (Fransson+2016) Up until 2016, only CO and SiO had been unambigously detected in SN spectra. Here, H2 was added as a third molecule in this group, using high-quality data for SN 1987A. H2 is important because it has a large UV opacity that will significantly change the radiation transport in the H zones. And since H material gets mixed into the core by Rayleigh Taylor, this affects not only the envelope but also the core. Future models need to consider this molecular opacity.