  We show that the delay between GRB170817A and GW170817 is incompatible with
de-beamed emission from an off-axis relativistic jet. The prompt emission and
the subsequent radio and X-ray observations can instead be interpreted within a
giant-flare-like scenario, being the result of a relativistic outflow driven by
the ultra-strong magnetic field produced by magnetohydrodynamic amplification
during the merger of the progenitor double neutron-star binary. Within such
picture, the data indicate that the outflow must be endowed with a steep
velocity profile, with a relatively fast tail extending to Gamma~8. Since the
conditions for the launch of such an outflow are quite general, and the
presence of a velocity profile is a natural expectation of the acceleration
process, most neutron star binary mergers should feature this quasi-isotropic,
hard X-ray emission component, that can be a powerful guide to the discovery of
additional kilonovae associated to relatively nearby gravitational wave events.
