http://arxiv.org/abs/1903.01466
We revisit the lower bound on binary tidal deformability tilde{Lambda} imposed by a luminous kilonova/macronova, AT 2017gfo, by numerical-relativity simulations of models consistent with gravitational waves from the binary-neutron-star merger, GW170817. Contrary to the claim made in the literature, we find that binaries with tilde{Lambda}<~400 can explain the luminosity of AT 2017gfo as far as moderate mass ejection from the remnant is assumed as also done in the previous work. The reason is that the maximum mass of a neutron star is not strongly correlated with tidal deformability of neutron stars with typical mass of ~1.4M_sun. If the maximum mass is so large that the binary does not collapse to a black hole immediately after merger, the mass of the ejecta can be sufficiently large irrespective of the binary tidal deformability. We explicitly present models of binary mergers with tilde{Lambda} down to 242 that satisfy the requirement on the mass of the ejecta from the luminosity of AT 2017gfo. We further find that the luminosity of AT 2017gfo could even be explained by models that do not experience bounce after merger. We conclude that the luminosity of AT 2017gfo is not very useful to constrain the binary tidal deformability. Accurate estimation of the mass ratio will be necessary to put a lower bound using electromagnetic counterparts in the future. We also caution that merger simulations performed employing a limited class of tabulated equations of state could be severely biased due to the lack of generality.
K. Kiuchi, K. Kyutoku, M. Shibata, et. al.
Wed, 6 Mar 19
62/75
Comments: 6 pages, 2 figures
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