  We study in detail the f-mode secular instability for rapidly rotating
neutron stars, putting emphasis on supermassive 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 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 Advance LIGO sensitivity at distance of about 20Mpc 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 post-merging
neutron stars and the strength of the magnetic fields.
