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#### Revisiting the lower bound on tidal deformability derived by AT 2017gfo

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1903.01466.pdf

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##### Citation

Kiuchi, K., Kyutoku, K., Shibata, M., & Taniguchi, K. (2019). Revisiting the lower
bound on tidal deformability derived by AT 2017gfo.* Astrophysical Journal,* *876*:
L31. doi:10.3847/2041-8213/ab1e45.

Cite as: https://hdl.handle.net/21.11116/0000-0003-576B-4

##### Abstract

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.

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.