An Explosion is Triggered by the Late Collapse of the Compact Remnant from a Neutron Star Merger

It is known that a binary neutron star (BNS) merger produces a hypermassive neutron star. The lifetime of this compact remnant depends on the total mass and the equation of state. The collapse of this compact remnant to a black hole torus system is expected to give rise to a powerful jet and a short gamma-ray burst. Nevertheless, if the collapse is delayed half a second or so, the surrounding matter would already be accreted and/or expelled, hence no significant torus is formed. However, the collapse itself gives rise to a quasi-isotropic magnetized fireball. This magnetic bomb dissipates much of its energy due to magnetic reconnection and produces the prompt emission. The energy range of such an explosion depends on the initial magnetic field strength and the amplification of the magnetic energy during merger. We briefly estimate the physical parameters at the time of collapse. We discuss the production of a quasi-isotropic magnetized fireball and its subsequent interaction with the ejected matter during merger as the outcome of the coalescence of a BNS system. We further suggest the radial stratification of the outflow, following the quasi-normal modes of the black hole.