Gravitational energy-momentum on nonmaximal surfaces

Gravitational Cauchy data defined iteratively from an input set which is of pure linearized gauge form representing a nonflat hypersurface appear to possess tachyonic energy-momentum $P^{\mu }$. We show that such systems do behave correctly: $P^{\mu }$ is positive timelike, and vanishing of the energy implies flat space. Although the $P^{\mu }$ begin at quartic order in the inputs, it is possible to exhibit explicitly the helicity-2 character of the gravitational excitations on which both the energy and the flatness conditions depend.