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Astrophysics, High Energy Astrophysical Phenomena, astro-ph.HE,General Relativity and Quantum Cosmology, gr-qc
Abstract:
We implement advanced Riemann solvers HLLC and HLLD
\cite{Mignone:2005ft,MUB:2009} together with an advanced constrained transport
scheme \cite{Gardiner:2007nc} in a numerical-relativity neutrino-radiation
magnetohydrodynamics code. We validate our implementation by performing a
series of one- and multi-dimensional test problems for relativistic
hydrodynamics and magnetohydrodynamics in both Minkowski spacetime and a static
black hole spacetime. We find that the numerical solutions with the advanced
Riemann solvers are more accurate than those with the HLLE solver
\cite{DelZanna:2002rv}, which was originally implemented in our code. As an
application to numerical relativity, we simulate an asymmetric binary neutron
star merger leading to a short-lived massive neutron star both with and without
magnetic fields. We find that the lifetime of the rotating massive neutron star
formed after the merger and also the amount of the tidally-driven dynamical
ejecta are overestimated when we employ the diffusive HLLE solver. We also find
that the magnetorotational instability is less resolved when we employ the HLLE
solver because of the solver's large numerical diffusivity. This causes a
spurious enhancement both of magnetic winding resulting from large scale
poloidal magnetic fields, and also of the energy of the outflow induced by
magnetic pressure.
