Radiative Transfer Simulation for the Optical and Near-infrared Electromagnetic Counterparts to GW170817

Recent detection of gravitational waves from a binary neutron star merger (GW170817) and the subsequent observations of electromagnetic counterparts provide a great opportunity to study the physics of compact binary mergers. The optical and near-infrared counterparts to GW170817 (SSS17a, also known as AT 2017gfo or DLT17ck) are found to be consistent with a kilonova/macronova scenario with red and blue components. However, in most previous studies wherein the contribution from each ejecta component to the lightcurves is separately calculated and composited, the red component is too massive of a dynamical ejecta, and the blue component is too fast of a post-merger ejecta. In this Letter, we perform a two-dimensional radiative transfer simulation for a kilonova/macronova, consistently taking the interplay of multiple ejecta components into account. We show that the lightcurves and photospheric velocity of SSS17a can be reproduced naturally by a setup that is consistent with the prediction of the numerical-relativity simulations.