Analytic models of the spectral properties of gravitational waves from neutron star merger remnants

We present a new analytic model describing gravitational-wave emission in the postmerger phase of binary neutron star mergers. The model is described by a number of physical parameters that are related to various oscillation modes, quasilinear combination tones or nonlinear features that appear in the postmerger phase. The time evolution of the main postmerger frequency peak is taken into account and it is described by a two-segment linear expression. The effectiveness of the model, in terms of the fitting factor or, equivalently, the reduction in the detection rate, is evaluated along a sequence of equal-mass simulations of varying mass. We find that all parameters of the analytic model correlate with the total binary mass of the system. For high masses, we identify new spectral features originating from the nonlinear coupling between the quasiradial oscillation and the antipodal tidal deformation, the inclusion of which significantly improves the fitting factors achieved by the model. We can thus model the postmerger gravitational-wave emission with an analytic model that achieves high fitting factors for a wide range of total binary masses. Our model can be used for the detection and parameter estimation of the postmerger phase in upcoming searches with upgraded second-generation detectors, such as aLIGO+ and aVirgo+, with future, third-generation detectors (Einstein Telescope and Cosmic Explorer) or with dedicated, high-frequency detectors.