  Binary neutron-star mergers have long been associated with short-duration
gamma-ray bursts (GRBs). This connection was confirmed with the first
coincident detection of gravitational waves together with electromagnetic
radiation from GW170817. The basic paradigm for short-duration GRBs includes an
ultra-relativistic jet, but the low-luminosity prompt emission together with
follow-up radio and X-ray observations have hinted that this picture may be
different in the case of GW170817. In particular, it has been proposed that
large amounts of the magnetic energy that is amplified after the merger, can be
released when the remnant collapses to a black hole, giving rise to a
quasi-spherical explosion impacting on the merger ejecta. Through numerical
simulations we investigate this scenario for a range of viewing angles,
injected energies and matter densities at the time of the collapse. Depending
on the magnitude of the energy injection and the remnant density, we find two
types of outflows: one with a narrow relativistic core and one with a
wide-angle, but mildly relativistic outflow. Furthermore, very wide outflows
are possible, but require energy releases in excess of 10^52 erg.
