Time-delay interferometry noise transfer functions for LISA

Abstract

The Laser Interferometry Space Antenna (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 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 step 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 noise. 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 this study, we present an update model for the beams, measurements and TDI, with several approximations to derive the noise transfer functions. The laser locking and noise correlation are taken into account to see their impact in the transfer functions. A methodology for such a derivation has been established in details, as well as verification procedures against simulated data. 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