Jet–Environment Interaction after Delayed Collapse in Binary Neutron Star Mergers

Abstract We present general relativistic magnetohydrodynamic simulations of binary neutron star mergers, where the collapse of the metastable massive neutron star (MNS) remnant leads to the production of an incipient jet having terminal Lorentz factor and Poynting-flux luminosity compatible with a short gamma-ray burst. We consider different MNS lifetimes of about 25 and 50 ms, long enough for massive polar outflows to emerge before black hole (BH) formation. The interaction of the following BH-driven jet with such polar outflows, responsible for shock heating and possible electromagnetic signatures, is self-consistently captured for the first time. Exploiting an unprecedentedly low numerical density floor scaling as r −6 , we explore the jet propagation up to distances of ∼10 4 km. Comparing the outcome of different MNS lifetimes, we find that the latter, by strongly affecting the propagation environment, plays a major role in determining the final properties of the escaping jet. Finally, we consider a noncollapsing case, where the MNS-driven outflow is found to exhibit a much higher density and lower velocity compared to the BH-driven jet.