Kilonova from post-merger ejecta as an optical and near-Infrared counterpart of GW170817

Recent detection of gravitational waves from a neutron star (NS) merger event GW170817 and identification of an electromagnetic counterpart provide a unique opportunity to study the physical processes in NS mergers. To derive properties of ejectedmaterial from the NS merger, we perform radiative transfer simulations of kilonova, optical and near-infrared emissions powered by radioactive decaysof r-processnuclei synthesized in the merger. We find that the observed near-infrared emission lasting for >10 d is explained by 0.03 M⊙ of ejectacontaining lanthanide elements. However, the blue optical component observed at the initial phases requires an ejectacomponent with a relatively high electron fraction (Ye). We show that both optical and near-infrared emissions are simultaneously reproduced by the ejectawith a medium Ye of ∼0.25. We suggest that a dominant component powering the emission is post-merger ejecta, which exhibits that the mass ejectionafter the first dynamical ejectionis quite efficient. Our results indicate that NS mergers synthesize a wide range of r-processelements and strengthen the hypothesis that NS mergers are the origin of r-processelements in the Universe.