Jet-like structures in low-mass binary neutron star merger remnants

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Milton Ruiz (University of Valencia)

GW170817 and GRB 170817A provided direct evidence that binary neutron star (NSNS) mergers can produce short gamma-ray bursts (sGRBs). However, questions remain about the nature of the central engine. Depending on the mass, the merger remnant may promptly collapse to a black hole (BH), form a hypermassive star which undergoes a delayed collapse to a BH after several tens of rotation periods, a supramassive star with a much longer lifetime, or an indefinitely stable sub-supramassive NS. We have performed general relativistic magnetohydrodynamics (GRMHD) simulations of the merger of both irrotational and spinning, equal-mass NSNSs constructed from a realistic SLy equation of state, with a range of gravitational (ADM) masses from 1.96 to 2.70 MSun. Each NS is endowed with a dipolar magnetic field extending from the interior into the exterior, as in a radio pulsar. The remnants are sub-supramassive for the lowest mass case, supramassive for the intermediate cases and hypermassive for the highest mass case. The latter is the only case that collapses to a BH before our simulation ends. We observe helical magnetic field structures and mildly relativistic outflow from the poles for both the supramassive and hypermassive remnants, and are investigating whether these jet-like structures can be the progenitors of sGRBs.