Dynamical ejecta of neutron star mergers with nucleonic weak processes II: Kilonova emission. (arXiv:2109.14617v4 [astro-ph.HE] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Just_O/0/1/0/all/0/1">Oliver Just</a> (1,2), <a href="http://arxiv.org/find/astro-ph/1/au:+Kullmann_I/0/1/0/all/0/1">Ina Kullmann</a> (3), <a href="http://arxiv.org/find/astro-ph/1/au:+Goriely_S/0/1/0/all/0/1">Stephane Goriely</a> (3), <a href="http://arxiv.org/find/astro-ph/1/au:+Bauswein_A/0/1/0/all/0/1">Andreas Bauswein</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Janka_H/0/1/0/all/0/1">Hans-Thomas Janka</a> (4), <a href="http://arxiv.org/find/astro-ph/1/au:+Collins_C/0/1/0/all/0/1">Christine E. Collins</a> ((1) GSI Darmstadt, (2) ABBL RIKEN, Saitama, (3) ULB Brussels, (4) MPA Garching)
The majority of existing results for the kilonova (or macronova) emission
from material ejected during a neutron-star (NS) merger is based on
(quasi-)one-zone models or manually constructed toy-model ejecta
configurations. In this study we present a kilonova analysis of the material
ejected during the first ~10ms of a NS merger, called dynamical ejecta, using
directly the outflow trajectories from general relativistic smoothed-particle
hydrodynamics simulations including a sophisticated neutrino treatment and the
corresponding nucleosynthesis results, which have been presented in Part I of
this study. We employ a multi-dimensional two-moment radiation transport scheme
with approximate M1 closure to evolve the photon field and use a heuristic
prescription for the opacities found by calibration with atomic-physics based
reference results. We find that the photosphere is generically ellipsoidal but
augmented with small-scale structure and produces emission that is about 1.5-3
times stronger towards the pole than the equator. The kilonova typically peaks
after 0.7-1.5days in the near-infrared frequency regime with luminosities
between 3-7×10^40erg/s and at photospheric temperatures of 2.2-2.8×10^3K. A
softer equation of state or higher binary-mass asymmetry leads to a longer and
brighter signal. Significant variations of the light curve are also obtained
for models with artificially modified electron fractions, emphasizing the
importance of a reliable neutrino-transport modeling. None of the models
investigated here, which only consider dynamical ejecta, produces a transient
as bright as AT2017gfo. The near-infrared peak of our models is incompatible
with the early blue component of AT2017gfo.
The majority of existing results for the kilonova (or macronova) emission
from material ejected during a neutron-star (NS) merger is based on
(quasi-)one-zone models or manually constructed toy-model ejecta
configurations. In this study we present a kilonova analysis of the material
ejected during the first ~10ms of a NS merger, called dynamical ejecta, using
directly the outflow trajectories from general relativistic smoothed-particle
hydrodynamics simulations including a sophisticated neutrino treatment and the
corresponding nucleosynthesis results, which have been presented in Part I of
this study. We employ a multi-dimensional two-moment radiation transport scheme
with approximate M1 closure to evolve the photon field and use a heuristic
prescription for the opacities found by calibration with atomic-physics based
reference results. We find that the photosphere is generically ellipsoidal but
augmented with small-scale structure and produces emission that is about 1.5-3
times stronger towards the pole than the equator. The kilonova typically peaks
after 0.7-1.5days in the near-infrared frequency regime with luminosities
between 3-7×10^40erg/s and at photospheric temperatures of 2.2-2.8×10^3K. A
softer equation of state or higher binary-mass asymmetry leads to a longer and
brighter signal. Significant variations of the light curve are also obtained
for models with artificially modified electron fractions, emphasizing the
importance of a reliable neutrino-transport modeling. None of the models
investigated here, which only consider dynamical ejecta, produces a transient
as bright as AT2017gfo. The near-infrared peak of our models is incompatible
with the early blue component of AT2017gfo.
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