Synergy between ground- and space-based gravitational-wave detectors for estimation of binary coalescence parameters

We study the advantages of the coexistence of future ground- and space-based gravitational-wave detectors in estimating the parameters of a binary coalescence. Space measurements will act as a precursor to ground measurements. Also, since space measurements will provide much better localization information on the source, they will aid electromagnetic follow-up of the source and hence increase the probability of finding an electromagnetic counterpart of the gravitational-wave event. Using the post-Newtonian waveform for the inspiral of nonspinning neutron star–black hole binaries in circular orbits, we analyze how estimates for the chirp mass, the symmetric mass ratio, and the time and phase at coalescence are improved by combining the data from different space–ground detector pairs. Since the gravitational waves produced by binary coalescence also provide a suitable domain where we can investigate strong field gravity, we also study the deviations from general relativity using the parameterized post-Einsteinian framework. As an example, focusing on the Einstein telescope and DECIGO pair, we demonstrate that there exists a sweet-spot range of sensitivity in the pre-DECIGO period where the best enhancement due to the synergy effect can be obtained for estimates of the post-Newtonian waveform parameters. Similar results are obtained for the parameter that characterizes deviation from general relativity