Gravitational wave afterglow in binary neutron star mergers

We study in detail the f-mode secular instability for rapidly rotating neutron stars, putting emphasis on supramassive models which do not have a stable nonrotating counterpart. Such neutron stars are thought to be the generic outcome of the merger of two standard-mass neutron stars. In addition, we take into account the effects of a strong magnetic field and r-mode instability, that can drain a substantial amount of angular momentum. We find that the gravitational wave signal emitted by supramassive neutron stars can reach above the Advanced LIGO sensitivity at distance of about 20 Mpc, and the detectability is substantially enhanced for the Einstein Telescope. The event rate will be of the same order as the merging rates, while the analysis of the signal will carry information for the equation of state of the postmerging neutron stars and the strength of the magnetic fields.