r-PROCESS LANTHANIDE PRODUCTION AND HEATING RATES IN KILONOVAE

By Jonas Lippuner, Luke F. Roberts. 2015

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r-process nucleosynthesis in material ejected during neutron star mergers may lead to radioactively powered transients called kilonovae. The timescale and peak luminosity of these transients depend on the composition of the ejecta, which determines the local heating rate from nuclear decays and the opacity. Kasen et al. and Tanaka & Hotokezaka pointed out that lanthanides can drastically increase the opacity in these outflows. We use the new general-purpose nuclear reaction network SkyNet to carry out a parameter study of r-process nucleosynthesis for a range of initial electron fractions Ye, initial specific entropies s, and expansion timescales τ. We find that the ejecta is lanthanide-free for Ye ≳ 0.22−0.30, depending on s and τ. The heating rate is insensitive to s and τ, but certain, larger values of Ye lead to reduced heating rates, due to individual nuclides dominating the heating. We calculate approximate light curves with a simplified gray radiative transport scheme. The light curves peak at about a day (week) in the lanthanide-free (-rich) cases. The heating rate does not change much as the ejecta becomes lanthanide-free with increasing Ye, but the light-curve peak becomes about an order of magnitude brighter because it peaks much earlier when the heating rate is larger. We also provide parametric fits for the heating rates between 0.1 and 100 days, and we provide a simple fit in Ye, s, and τ to estimate whether or not the ejecta is lanthanide-rich.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/eff2d0c8d601dbbc94a25e837267803127287d63

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Citations in the corpus

Colloquium : Superheavy elements: Oganesson and beyond (2019, background): “These high neutron densities allow the seed nuclei that are present in the environment to undergo multiple neutron captures before beta decaying, leading to the synthesis of neutron-rich nuclei (see also (Freiburghaus et al., 1999; Goriely, 2015; Lippuner and Roberts, 2015; Mendoza-Temis et al., 201”
Binary Neutron Star Mergers: Mass Ejection, Electromagnetic Counterparts, and Nucleosynthesis (2018, background): “26R R 0 0, 3 r r= - ⎜ ⎟⎛⎝ ⎞ ⎠( ) ( ) This density history is matched with the expansion histories used in the parameterized r-process calculations of Lippuner & Roberts (2015): t s Y T et , , 6 GK 3 , 27e0 0 3 r r t = = ⎜ ⎟ ⎛ ⎝ ⎞ ⎠( ) ( ) ( ) where e;2.718 is Euler’s number.”
The Origin of r-process Elements in the Milky Way (2017, background): “…ejecta should have a higher electron fraction (Ye = 0.2 − 0.5) than the dynamical ejecta, thus producing isotopes in the range between the 1st and 2nd r-process peaks, or even near the iron peak for particularly high Ye values (Lippuner & Roberts 2015; Lippuner et al. 2017; Martin et al. 2015).”
Dynamical Mass Ejection from Binary Neutron Star Mergers (2016, methodology): “At late times, the density history used in Lippuner & Roberts (2015) has the form ρ(t) = ρ(s, Ye, T = 6 GK)(3τ/et) 3, where e is Euler’s number.”
Impact of ejecta morphology and composition on the electromagnetic signatures of neutron star mergers (2017, background): “The influence of the radioactive heating rates was studied by Lippuner & Roberts (2015), who found that the heating profile remains quite featureless (see also Barnes et al. 2016; Rosswog et al. 2017; Wu et al. 2016).”
THE LIGHT CURVE OF THE MACRONOVA ASSOCIATED WITH THE LONG–SHORT BURST GRB 060614 (2015, background): “Moreover, the poorly-constrained electron fraction (Ye), the escape velocity distribution and the anisotropy of the outflow play additional roles in shaping the macronova emission (Tanaka et al. 2014; Lippuner & Roberts 2015), are all caveats that should be considered when interpreting our results.”
Production of the entire range of r-process nuclides by black hole accretion disc outflows from neutron star mergers (2016, background): “As a result, we do not recover the entropy dependence obtained in parametrized nucleosynthesis studies such as Lippuner & Roberts (2015).”
Signatures of hypermassive neutron star lifetimes on r-process nucleosynthesis in the disc ejecta from neutron star mergers (2017, background): “Also shown is the amount of mass ejected with Ye,5GK 6 0.25, which is neutron-rich enough to robustly make the full r-process (see next section and, e.g., Lippuner & Roberts 2015).”
Three-dimensional GRMHD Simulations of Neutrino-cooled Accretion Disks from Neutron Star Mergers (2017, unknown): “0.25 (Lippuner & Roberts 2015).”
A Magnetar Origin for the Kilonova Ejecta in GW170817 (2018, background): “4 matter is dominated by a few discrete nuclei (Lippuner & Roberts 2015), inconsistent with the observed smooth decay of the KN bolometric light curve (Rosswog et al. 2017).”