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

TL;DR

This paper estimates the excitation amplitudes of neutron star vibrational modes caused by magnetar giant flares, finding that crustal modes are strongly excited but f-modes are weakly excited, making gravitational wave detection unlikely.

Contribution

It provides the first estimates of post-flare amplitudes of both crustal torsional modes and global f-modes in magnetars, highlighting their excitation levels and detection prospects.

Findings

Crustal torsional modes can be strongly excited by flares.

Only a small fraction of flare energy excites f-modes.

Detection of f-modes with advanced LIGO is unlikely.

Abstract

Magnetar giant flares may excite vibrational modes of neutron stars. Here we compute an estimate of initial post-flare amplitudes of both 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 about 10^{15} Gauss, the gravitational-wave detection of these f-modes with advanced LIGO is unlikely.