On the excitation of f modes and torsional modes by magnetar giant flares

Magnetar giant flares may excite vibrational modes of neutron stars. Here we compute an estimate of initial post-flare amplitudes both of the torsional modes in the magnetar’s crust and of the global f modes. We show that while the torsional crustal modes can be strongly excited, only a small fraction of the flare’s energy is converted directly into the lowest order f modes. For a conventional model of a magnetar, with the external magnetic field of ∼1015 G, the gravitational wave detection of these f modes with Advanced LIGO is unlikely.