AT2017gfo: an anisotropic and three-component kilonova counterpart of GW170817

Abstract

The detection of a kilo/macronova electromagnetic counterpart (AT2017gfo) of the first gravitational wave signal compatible with the merger of two neutron stars (GW170817) has confirmed the occurrence of r-process nucleosynthesis in this kind of events. The blue and red components of AT2017gfo have been interpreted as the signature of multi-component ejecta in the merger dynamics. However, the explanation of AT2017gfo in terms of the properties of the ejecta and of the ejection mechanisms is still incomplete. In this work, we analyse AT2017gfo with a new semi-analytic model of kilo/macronova inferred from general relativistic simulations of the merger and long-term numerical models of the merger aftermath. The model accounts for the anisotropic emission from the three known mass ejecta components: dynamic, winds and secular outflows from the disk. The early multi-band light-curves of AT2017gfo can only be explained by the presence of a relatively low opacity component of the ejecta at high latitudes. This points to the key role of weak interactions in setting the ejecta properties and determining the nucleosynthetic yields. Our model constrains also the total ejected mass associated to AT2017gfo to be between $0.042$ and $0.077 M_{\odot}$; the observation angle of the source to be between $π/12$ and $7π/36 $; and the mass of the disk to be $ \gtrsim 0.08 M_{\odot}$.