The Astrophysical Journal Letters (Jan 2023)
The Collimation of Relativistic Jets in Post–Neutron Star Binary Merger Simulations
Abstract
The gravitational waves from the binary neutron star merger GW170817 were accompanied by a multiwavelength electromagnetic counterpart, which confirms the association of the merger with a short gamma-ray burst (sGRB). The afterglow observations implied that the event was accompanied by a narrow, ∼5°, and powerful, ∼10 ^50 erg, jet. We study the propagation of a Poynting flux–dominated jet within the merger ejecta (kinematic, neutrino-driven, and magnetorotational instability turbulence-driven) of a neutrino-radiation-GRMHD simulation of two coalescing neutron stars. We find that the presence of a postmerger low-density/low-pressure polar cavity, which arose due to angular momentum conservation, is crucial to let the jet break out. At the same time the ejecta collimates the jet to a narrow opening angle. The collimated jet has a narrow opening angle of ∼4°–7° and an energy of 10 ^49 –10 ^50 erg, in line with the observations of GW170817 and other sGRBs.
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