Numerical simulations of neutron star mergers as the central engines of short-period gamma-ray bursts
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Date
2009Author
Archibald, Richard Andrew
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Abstract
We present the results of fully three dimensional, post-Newtonian hydrodynamical
simulations of the dynamical evolution of mergers between compact stellar remnants
(neutron stars and black holes). Although the code is essentially Newtonian, we
simulate gravitational wave emission and the corresponding effect on the fluid flow
via a post-Newtonian correction. Also, we use a modified Newtonian potential which
reproduces certain aspects of the Schwarzschild and Kerr solutions to improve the
physics in the vicinity of the black hole. Changes to the energy by neutrino/antineutrino
emission are accounted for by an extensive neutrino leakage scheme. The
hydrodynamical equations are integrated using the piecewise parabolic method (PPM)
and the neutron star matter is described by a tabulated equation of state (EoS).
Since the physics of matter at the extreme densities found in neutron stars is not yet
certain, we compare results computed using two such tables to ascertain whether this
uncertainty in the micro-physics extends to an uncertainty in the energy available to
power a short-period gamma-ray burst.
With an aim to including magnetic field physics to these simulations, we present
a survey of approximate Riemann solvers which may be more easily extended to the
system of equations of magnetohydrodynamics (MHD) than the exact or iterative
Riemann solver used in the PPM scheme. Tests are performed using the linearised
solver of Roe and the approximate Harten, Lax, van Leer and Einfeldt Riemann
solvers (HLLE and HLLEM) with the PPM reconstruction scheme. Finally, we discuss
the effectiveness of these approximate Riemann solvers in the simulation of mergers
between compact stellar remnants.