Predicting Kilonovae From LVK Gravitational Wave Candidates

Abstract

Kilonovae, the electromagnetic signature resulting from the merger of two neutron stars or a neutron star and a black hole, are sources for r-process nucleosynthesis and can therefore provide information on how heavy elements are produced in the universe. Studying kilonovae is difficult due to their short-lived nature and rarity, so it is valuable to astronomers to be able to predict when and where in the sky kilonovae may occur. This can be done by analyzing gravitational wave candidates detected by the LIGO-Virgo-KAGRA (LVK) collaboration. Gravitational waves are fluctuations in space-time, usually produced by merging black holes and/or neutron stars, and provide information on the masses of the merging objects. We implement a method that uses this information to produce potential kilonovae light curves for gravitational wave candidates, which helps to discern which candidates merit a followup search for electromagnetic emissions. This method starts by using estimates of the mass and spin from the initial gravitational wave detection. Then, the mass of ejected matter is estimated by employing ejecta fits and marginalizing over 10,000 possible neutron star equation of states. Finally, sample inclination angles and a range of light curves are then produced for the gravitational wave candidate. We find that the 90% credible interval of these light curves for a given gravitational wave candidate will most likely contain the light curve produced for that candidate using the SLy equation of state, which is an equation of state supported by observations of GW170817, the only joint detection of a gravitational wave signal and its kilonova. This demonstrates that the method presented produces light curves consistent with our current knowledge, and we hope our predictions can aid astronomers in determining which gravitational wave candidates will produce kilonovae, and what these kilonovae will look like.