Viscous hydrodynamic evolution of neutron star merger accretion disks: a code comparison
arxiv(2023)
摘要
The accretion disk formed after a neutron star merger is an important
contributor to the total ejecta from the merger, and hence to the kilonova and
the r-process yields of each event. Axisymmetric viscous hydrodynamic
simulations of these disks can capture thermal mass ejection due to neutrino
absorption and in the advective phase – after neutrino cooling has subsided –
and are thus likely to provide a lower-limit to the total disk ejecta relative
to MHD evolution. Here we present a comparison between two viscous hydrodynamic
codes that have been used extensively on this problem over the past decade:
ALCAR and FLASH. We choose a representative setup with a black hole at the
center, and vary the treatment of viscosity and neutrino transport. We find
good overall agreement (∼ 10% level) in most quantities. The average
outflow velocity is sensitive to the treatment of the nuclear binding energy of
heavy nuclei, showing a larger variation than other quantities. We post-process
trajectories from both codes with the same nuclear network, and explore the
effects of code differences on nucleosynthesis yields, heating rates, and
kilonova light curves. For the latter, we also assess the effect of varying the
number of tracer particles in reconstructing the spatial abundance distribution
for kilonova light curve production.
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