Choosing a waveform approximant

The modelling of gravitational waveforms is complex, and no single model (“approximant”) at the moment captures all relevant physics for a generic analysis. Some models are natively implemented in GWFish, and they can be accessed by using the waveform class GWFish.modules.<waveform_name>, where waveform_name is one of the following (explained later):

• 'TaylorF2';

• 'IMRPhenomD'.

Many more models are available by calling LALSimulation, a code developed by the LIGO-Virgo-Kagra collaboration. It should be automatically installed, as the python package lalsuite, together with GWFish.

In order to use these models in GWFish, specify the waveform class GWFish.modules.LALFD_Waveform, and then the name of the model, such as 'IMRPhenomD'. For a complete list of options, see here. Some models that are commonly used in our analyses are:

• 'TaylorF2', a simple and analytic post-Newtonian approximant, used when we only care about the low-frequency part of the signal which is unaffected by high-order effects;

• 'IMRPhenomD', a tuned high-order approximant for black hole binaries without higher order modes, the default choice in GWFish;

• 'IMRPhenomXPHM', a similar model also including higher order modes (especially important for high-mass and off-axis events);

• 'IMRPhenomD_NRTidalv2', a model for neutron star binaries including tidal effects.