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Abstract

We have studied the dynamics of an equal-mass magnetized neutron-star binary
within a resistive magnetohydrodynamic (RMHD) approach in which the highly
conducting stellar interior is matched to an electrovacuum exterior. Because
our analysis is aimed at assessing the modifications introduced by resistive
effects on the dynamics of the binary after the merger and through to collapse,
we have carried out a close comparison with an equivalent simulation performed
within the traditional ideal magnetohydrodynamic approximation. We have found
that there are many similarities between the two evolutions but also one
important difference: the survival time of the hyper massive neutron star
increases in a RMHD simulation. This difference is due to a less efficient
magnetic-braking mechanism in the resistive regime, in which matter can move
across magnetic-field lines, thus reducing the outward transport of angular
momentum. Both the RMHD and the ideal magnetohydrodynamic simulations carried
here have been performed at higher resolutions and with a different grid
structure than those in previous work of ours [L. Rezzolla, B. Giacomazzo, L.
Baiotti, J. Granot, C. Kouveliotou, and M. A. Aloy, Astrophys. J. Letters 732,
L6 (2011)], but confirm the formation of a low-density funnel with an ordered
magnetic field produced by the black hole--torus system. In both regimes the
magnetic field is predominantly toroidal in the highly conducting torus and
predominantly poloidal in the nearly evacuated funnel. Reconnection processes
or neutrino annihilation occurring in the funnel, none of which we model, could
potentially increase the internal energy in the funnel and launch a
relativistic outflow, which, however, is not produced in these simulations.