A Low-mass Binary Neutron Star: Long-term Ejecta Evolution and Kilonovae with Weak Blue Emission

Kyohei Kawaguchi, Sho Fujibayashi, Masaru Shibata, Masaomi Tanaka, Shinya Wanajo

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24 Citations (Scopus)


We study the long-term evolution of ejecta formed in a binary neutron star (NS) merger that results in a long-lived remnant NS by performing a hydrodynamics simulation with the outflow data of a numerical relativity simulation as the initial condition. At the homologously expanding phase, the total ejecta mass reaches ≈ 0.1 M o˙ with an average velocity of ≈ 0.1 c and lanthanide fraction of ≈ 0.005. We further perform the radiative transfer simulation employing the obtained ejecta profile. We find that, contrary to a naive expectation from the large ejecta mass and low lanthanide fraction, the optical emission is not as bright as that in GW170817/AT2017gfo, while the infrared emission can be brighter. This light-curve property is attributed to preferential diffusion of photons toward the equatorial direction due to the prolate ejecta morphology; large opacity contribution of Zr, Y, and lanthanides; and low specific heating rate of the ejecta. Our results suggest that these light-curve features could be used as an indicator for the presence of a long-lived remnant NS. We also found that the bright optical emission broadly consistent with GW170817/AT2017gfo is realized for the case in which the high-velocity ejecta components in the polar region are suppressed. These results suggest that the remnant in GW170817/AT2017gfo is unlikely to be a long-lived NS but might have collapsed to a black hole within O (0.1) s.

Original languageEnglish
Article number100
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 2021 Jun 1

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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