Dynamical ejecta of neutron star mergers with nucleonic weak processes – II: kilonova emission

Just, Oliver; Kullmann, I. K. B.; Goriely, Stéphane; Bauswein, Andreas; Janka, Hans-Thomas; Collins, Christine E.

doi:10.1093/mnras/stab3327

Cited by 36 publications

(25 citation statements)

References 136 publications

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“…In neutron star mergers, the heaviest elements are produced mainly in the tidal ejecta component, i.e., in the ejecta that is mostly distributed toward the equatorial plane (e.g., Bauswein et al 2013;Just et al 2015;Sekiguchi et al 2015;Kullmann et al 2022;Just et al 2022). Hence, the kilonova observed in the equatorial direction is likely to show the effect of the presence of lanthanides.…”

Section: Modelmentioning

confidence: 99%

Opacity of the Highly Ionized Lanthanides and the Effect on the Early Kilonova

Banerjee

Tanaka

Kato

et al. 2022

ApJ

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We investigate the effect of the presence of lanthanides (Z = 57–71) on the kilonova at t ∼ 1 hr after the neutron star merger for the first time. For this purpose, we calculate the atomic structures and the opacities for selected lanthanides: Nd (Z = 60), Sm (Z = 62), and Eu (Z = 63). We consider the ionization degree up to 10th (XI), applicable for the ejecta at t ∼ a few hours after the merger, when the temperature is T ∼ 105 K. We find that the opacities for the highly ionized lanthanides are exceptionally high, reaching κ exp ∼ 1000 cm 2 g − 1 for Eu, due to the highly dense energy levels. Using the new opacity, we perform radiative transfer simulations to show that the early light curves become fainter by a (maximum) factor of four, in comparison to lanthanide-free ejecta at t ∼ 0.1 days. However, the period at which the light curves are affected is relatively brief owing to the rapid time evolution of the opacity in the outermost layer of the ejecta. We predict that for a source at a distance of ∼100 Mpc, UV brightness for lanthanide-rich ejecta shows a drop to ∼21–22 mag at t ∼ 0.1 days and the UV peaks around t ∼ 0.2 days with a magnitude of ∼19 mag. Future detection of such a kilonova by an existing UV satellite like Swift or the upcoming UV satellite ULTRASAT will provide useful constraints on the abundance in the outer ejecta and the corresponding nucleosynthesis conditions in the neutron star mergers.

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Section: Modelmentioning

confidence: 99%

Opacity of the Highly Ionized Lanthanides and the Effect on the Early Kilonova

Banerjee

Tanaka

Kato

et al. 2022

ApJ

View full text Add to dashboard Cite

show abstract

“…In neutron star merger, the heaviest elements are produced mainly in the tidal ejecta component, i.e., in the ejecta that is mostly distributed towards the equatorial plane (e.g., Bauswein et al 2013;Just et al 2015;Sekiguchi et al 2015;Kullmann et al 2022;Just et al 2022). Hence, the kilonova observed in the equatorial direction is likely to show the effect of the presence of lanthanides.…”

Section: Modelmentioning

confidence: 99%

Opacity of the highly ionized lanthanides and the effect on the early kilonova

Banerjee,

Tanaka,

Kato

et al. 2022

Preprint

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We investigate the effect of the presence of lanthanides (Z = 57 − 71) on the kilonova at t ∼ hours after the neutron star merger for the first time. For this purpose, we calculate the atomic structures and the opacities for selected lanthanides: Nd (Z = 60), Sm (Z = 62), and Eu (Z = 63). We consider the ionization degree up to tenth (XI), applicable for the ejecta at t ∼ a few hours after the merger, when the temperature is T ∼ 10 5 K. We find that the opacities for the highly ionized lanthanides are exceptionally high, reaching κ exp ∼ 1000 cm 2 g −1 for Eu, thanks to the energy levels being highly dense. Using the new opacity, we perform radiative transfer simulations to show that the early light curves become fainter by a (maximum) factor of four, in comparison to lanthanide-free ejecta at t ∼ 0.1 day. However, the period at which the light curves are affected is relatively brief due to the rapid time evolution of the opacity in the outermost layer of the ejecta. We predict that for a source at a distance of ∼ 100 Mpc, UV brightness for lanthanide-rich ejecta shows a drop to ∼ 21 − 22 mag at t ∼ 0.1 day and the UV peaks around t ∼ 0.2 day with a magnitude of ∼ 19 mag. Future detection of such a kilonova by the existing UV satellite like Swift or the upcoming UV satellite ULTRASAT will provide useful constraints on the abundance in the outer ejecta and the corresponding nucleosynthesis conditions in the neutron star mergers.

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“…We then plug these data into the spherically symmetric version of the scheme described in Ref. [136], which solves the radiative transfer equations in the M1 approximation using simplified, parametrized opacities (see [136] for technical details of the solver). The right panels of Fig.…”

Section: Impact On Nucleosynthesis and Electromagnetic Counterpartmentioning

confidence: 99%

Fast Neutrino Conversion in Hydrodynamic Simulations of Neutrino-Cooled Accretion Disks

Just,

Abbar,

et al. 2022

Preprint

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The outflows from neutrino-cooled black-hole (BH) accretion disks formed in neutron-star mergers or cores of collapsing stars are expected to be neutron-rich enough to explain a large fraction of elements created by the rapid neutron-capture (r-) process, but their precise chemical composition remains elusive. Here, we investigate the role of fast neutrino flavor conversion, motivated by the findings of our post-processing analysis that shows evidence of electron-neutrino lepton-number (ELN) crossings deep inside the disk, hence suggesting possibly non-trivial effects due to neutrino flavor mixing. We implement a parametric, dynamically self-consistent treatment of fast conversion in time-dependent simulations and examine the impact on the disk and its outflows. By activating the, otherwise inefficient, emission of heavy-lepton neutrinos, fast conversions enhance the disk cooling rates and reduce the absorption rates of electron-type neutrinos, causing a reduction of the electron fraction in the disk by 0.03 − 0.06 and in the ejected material by 0.01 − 0.03. The r-process yields are enhanced by typically no more than a factor of two, rendering the overall impact of fast conversions modest. The kilonova is prolonged as a net result of increased lanthanide opacities and enhanced radioactive heating rates. We observe only mild sensitivity to the disk mass, the condition for the onset of flavor conversion, and to the considered cases of flavor mixing. Remarkably, parametric models of flavor mixing that conserve the lepton numbers per family result in an overall smaller impact than models invoking three-flavor equipartition, often assumed in previous works.

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Dynamical ejecta of neutron star mergers with nucleonic weak processes – II: kilonova emission

Cited by 36 publications

References 136 publications

Opacity of the Highly Ionized Lanthanides and the Effect on the Early Kilonova

Opacity of the Highly Ionized Lanthanides and the Effect on the Early Kilonova

Opacity of the highly ionized lanthanides and the effect on the early kilonova

Fast Neutrino Conversion in Hydrodynamic Simulations of Neutrino-Cooled Accretion Disks

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