An explosion is triggered by the late collapse of the compact remnant from a neutron star merger

Abstract: It is known that a binary neutron star 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 be already accreted and/or expelled and hence no torus will be formed. However, the collapse itself will give rise to a quasi-isotropic magnetized fireball. This magnetic bomb will dissipate much of its energy due to magnetic re-connection and will produce the prompt emission, when the fireball will become transparent to gamma-rays. The energy range of such an explosion depends on the initial magnetic field strength of the two neutron stars and the amplification of the magnetic energy during merger. 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 binary neutron star system. We further discuss a possible origin for the duration of the burst and the radial stratification of the flow following the quasi-normal modes of the black hole.