Binary neutron star mergers can be sources of gravitational waves coincident with electromagnetic counterpart emission across the spectrum .
To solidify their role as multimessenger sources , we present fully 3D , general relativistic , magnetohydrodynamic simulations of highly spinning binary neutrons stars initially on quasicircular orbits that merge and undergo delayed collapse to a black hole .
The binaries consist of two identical stars modeled as \Gamma = 2 polytropes with spin \chi _ { \text { \tiny { NS } } } = 0.36 aligned along the direction of the total orbital angular momentum L .
Each star is initially threaded by a dynamical unimportant interior dipole magnetic field .
The field is extended into the exterior where a nearly force-free magnetosphere resembles that of a pulsar .
The magnetic dipole moment \mu is either aligned or perpendicular to L and has the same initial magnitude for each orientation .
For comparison , we also impose symmetry across the orbital plane in one case where \mu in both stars is aligned along L .
We find that the lifetime of the transient hypermassive neutron star remnant , the jet launching time , and the ejecta ( which can give rise to a detectable kilonova ) are very sensitive to the magnetic field orientation .
By contrast , the physical properties of the black hole + disk remnant , such as the mass and spin of the black hole , the accretion rate , and the electromagnetic ( Poynting ) luminosity , are roughly independent of the initial magnetic field orientation .
In addition , we find imposing symmetry across the orbital plane does not play a significant role in the final outcome of the mergers .
Our results suggest that , as in the black hole-neutron star merger scenario , an incipient jet emerges only when the seed magnetic field has a sufficiently large-scale poloidal component aligned to the initial orbital angular momentum .
The lifetime [ \Delta t \gtrsim 140 ( M _ { \text { \tiny { NS } } } / 1.625 M _ { \odot } ) ms ] and Poynting luminosities [ L _ { \text { \tiny EM } } \simeq 10 ^ { 52 } erg/s ] of the jet , when it forms , are consistent with typical short gamma ray bursts , as well as with the Blandford–Znajek mechanism for launching jets .