Higher memory effects and the post-Newtonian calculation of their gravitational-wave signals.

A new hierarchy of lasting gravitational-wave effects was recently identified in asymptotically flat spacetimes. The better-known displacement, spin, and center-of-mass memory effects were included in the lowest two orders in the set of these effects. These higher memory effects are determined by a set of temporal moments of the news tensor, describing radiation from an isolated source, and the moments of the news could be expressed in terms of changes in charge-like expressions, and integrals over retarded time of flux-like terms, which vanish in the absence of radiation. We compute expressions for the flux contribution to the moments of the news in terms of a set of multipole moments that characterize the gravitational-wave strain. In the context of post-Newtonian(PN) theory, we compute the leading PN expressions for the moments and show that the strain related to the moments of the news is responsible for the many nonlinear, instantaneous terms and memory terms that appear in the PN expressions for the radiative multipole moments of the strain. These results provide a new viewpoint on the waveforms computed from the PN formalism and could be used to assess the detection prospects of this new class of higher memory effects.