A detailed study of the impact of mass ejecta and velocity profiles on kilonova properties with GEMMA

The first observation of a binary neutron star merger GW170817/AT2017gfo ushered the world into a new era of multimessenger astronomy. The event elucidated many then-unknown properties of neutron star mergers, such as their nucleosynthetic yields and many aspects of their merger dynamics. However, many features of GW170817/AT2017gfo and binary neutron star mergers in general remain uncertain, including detailed information about the mass ejection processes. GEMMA is a state-of-the-art multimessenger analysis tool whose primary function is to provide forward and backward modeling of binary neutron star and neutron star-black hole mergers. Here, we expand upon GEMMA’s capabilities to accept a series of formulae derived from numerical relativity simulations for binary neutron star mass ejection and velocity profiles. We assume a two-component ejecta model consisting of dynamical ejecta and post-merger disk ejecta, which each have distinct observable properties. We then compare the relative performance of the ejecta models to each other and to AT2017gfo to identify predominant sources of uncertainty in kilonova lightcurves. We also vary intrinsic binary parameters, such as the mass ratio and tidal deformability, to ascertain their influence on the resultant lightcurves.