Properties of Kilonovae from Dynamical and Post-merger Ejecta of Neutron Star Mergers

Masaomi Tanaka, Daiji Kato, Gediminas Gaigalas, Pavel Rynkun, Laima Radžiute, Shinya Wanajo, Yuichiro Sekiguchi, Nobuyuki Nakamura, Hajime Tanuma, Izumi Murakami, Hiroyuki A. Sakaue

Research output: Contribution to journalArticlepeer-review

57 Citations (Scopus)

Abstract

Ejected material from neutron star mergers gives rise to electromagnetic emission powered by radioactive decays of r-process nuclei, the so-called kilonova or macronova. While properties of the emission are largely affected by opacities in the ejected material, available atomic data for r-process elements are still limited. We perform atomic structure calculations for r-process elements: Se (Z = 34), Ru (Z = 44), Te (Z = 52), Ba (Z = 56), Nd (Z = 60), and Er (Z = 68). We confirm that the opacities from bound-bound transitions of open f-shell, lanthanide elements (Nd and Er) are higher than those of the other elements over a wide wavelength range. The opacities of open s-shell (Ba), p-shell (Se and Te), and d-shell (Ru) elements are lower than those of open f-shell elements, and their transitions are concentrated in the ultraviolet and optical wavelengths. We show that the optical brightness can be different by mag depending on the element abundances in the ejecta such that post-merger, lanthanide-free ejecta produce brighter and bluer optical emission. Such blue emission from post-merger ejecta can be observed from the polar directions if the mass of the preceding dynamical ejecta in these regions is small. For the ejecta mass of 0.01 M, observed magnitudes of the blue emission will reach 21.0 mag (100 Mpc) and 22.5 mag (200 Mpc) in the g and r bands within a few days after the merger, which are detectable with 1 m or 2 m class telescopes.

Original languageEnglish
Article number109
JournalAstrophysical Journal
Volume852
Issue number2
DOIs
Publication statusPublished - 2018 Jan 10
Externally publishedYes

Keywords

  • gravitational waves
  • nuclear reactions, nucleosynthesis, abundances
  • opacity
  • radiative transfer
  • stars: neutron

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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