AT2018kzr: the merger of an oxygen-neon white dwarf and a neutron star or black hole

Understand

We present detailed spectroscopic analysis of the extraordinarily fast-evolving transient AT2018kzr.

• The transient's observed lightcurve showed a rapid decline rate, comparable to the kilonova AT2017gfo.
• We calculate a self-consistent sequence of radiative transfer models (using TARDIS) and determine that the ejecta material is dominated by intermediate-mass elements (O, Mg and Si), with a photospheric velocity of $\sim$12000-14500km/s.
• The early spectra have the unusual combination of being blue but dominated by strong FeII and FeIII absorption features.