Gravitational wave forms at finite distances and at null infinity

Abstract
Motivated by the methodology of numerical studies of gravitational radiation, we investigate the discrepancies that arise if wave forms are observed at a finite distance as opposed to infinity. Our study is based upon scalar radiation from a spherically symmetric Einstein-Klein-Gordon system. This allows us to isolate the effects of backscattering and redshifting while avoiding more complicated effects that arise in nonspherical systems with gravitational radiation. We show that discrepancies close to 100% can arise at large observation distances R>>M for sufficiently periodic systems. They are most pronounced for radiation losses between one-quarter and one-half of the initial mass. This falls within the expected regime of the spiral infall of a relativistic binary system. The predominant contribution to this discrepancy stems from a time-dependent redshift arising from radiative mass loss.

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