Neutron star mergers are unique laboratories of accretion , ejection , and r-process nucleosynthesis .
We used 3D general relativistic magnetohydrodynamic simulations to study the role of the post-merger magnetic geometry in the evolution of merger remnant discs around stationary Kerr black holes .
Our simulations fully capture mass accretion , ejection , and jet production , owing to their exceptionally long duration exceeding 4 s. Poloidal post-merger magnetic field configurations produce jets with energies E _ { \mathrm { jet } } \sim ( 4 { - } 30 ) \times 10 ^ { 50 } erg , isotropic equivalent energies E _ { \mathrm { iso } } \sim ( 4 { - } 20 ) \times 10 ^ { 52 } erg , opening angles \theta _ { \mathrm { jet } } \sim 6 { - } 13 ^ { \circ } , and durations t _ { j } \lesssim 1 s. Accompanying the production of jets is the ejection of f _ { \mathrm { ej } } \sim 30 { - } 40 \% of the post-merger disc mass , continuing out to times > 1 s. We discover that a more natural , purely toroidal post-merger magnetic field geometry generates large-scale poloidal magnetic flux of alternating polarity and striped jets .
The first stripe , of E _ { \mathrm { jet } } \simeq 2 \times 10 ^ { 48 } \mathrm { erg } , E _ { \mathrm { iso } } \sim 10 ^ { 51 } erg , \theta _ { \mathrm { jet } } \sim 3.5 { - } 5 ^ { \circ } , and t _ { j } \sim 0.1 s , is followed by \gtrsim 4 s of striped jet activity with f _ { \mathrm { ej } } \simeq 27 \% .
The dissipation of such stripes could power the short gamma-ray burst ( sGRB ) prompt emission .
Our simulated jet energies and durations span the range of sGRBs .
We find that although the blue kilonova component is initially hidden from view by the red component , it expands faster , outruns the red component , and becomes visible to off-axis observers .
In comparison to GW 170817/GRB 170817A , our simulations under-predict the mass of the blue relative to red component by a factor of few .
Including the dynamical ejecta and neutrino absorption may reduce this tension .