Time-delay interferometry noise transfer functions for LISA

The LISA mission is the future space-based gravitational wave (GW) observatory of the European Space Agency. It is formed by 3 spacecraft exchanging laser beams in order to form multiple real and virtual interferometers. The data streams to be used in order to extract the large number and variety of GW sources are Time-Delay Interferometry (TDI) data. One important processing to produce these data is the TDI on-ground processing which recombines multiple interferometric on-board measurements to remove certain noise sources from the data such as laser frequency noise or spacecraft jitter. The LISA noise budget is therefore expressed at the TDI level in order to account for the different TDI transfer functions applied for each noise source and thus estimate their real weight on mission performance. In order to derive a usable form of these transfer functions, a model of the beams, the measurements, and TDI have been developed, and several approximation have been made. A methodology for such a derivation has been established, as well as verification procedures. It results in a set of transfer functions, which are now used by the LISA project, in particular in its performance model. Using these transfer functions, realistic noise curves for various instrumental configurations are provided to data analysis algorithms and used for instrument design.