Persistent Gravitational Wave Observables from Post-Newtonian Compact Binaries.

Persistent gravitational wave (GW) observables are generalizations of the GW memory effect that contain time-integrated changes in the spacetime curvature between two non-radiative regions. In asymptotically flat space-times at leading order in luminosity distance, these observables are determined by different temporal moments of the time derivative of the GW strain (the news tensor). These moments arise predominantly from nonlinear terms in the Einstein equations that can be challenging to evaluate numerically or with high-order analytical calculations; however, they can be inferred from lower-order waveforms for which the moments vanish by sequentially integrating the Bondi-Sachs evolution and conservation equations. We use these equations to calculate the leading post-Newtonian (PN) contributions to the moments of the news for compact-binary sources. While these moments are measurable by observers in relative acceleration far from an isolated source, they are not easily accessible to current interferometric GW detectors, such as LIGO, which are calibrated to measure the GW strain. We therefore identify components of the GW strain that are responsible for these moments. We find that the PN order of these moments increases for higher-order moments of the news.