Probing soft signals of gravitational-wave memory with space-based interferometers

Abstract

Gravitational-wave displacement memory is a remarkable, ubiquitous prediction of general relativity that has not yet been detected. Unlike the oscillatory components of gravitational waveforms, displacement memory is associated with soft gravitons and provides the leading low-frequency observable of its parent event. Analogous soft signals may also be associated with velocity and integrated-displacement memory. The simple, universal spectral shapes of soft waveforms provide effective templates for matched filtering and parameter estimation. In this paper, we investigate the detection prospects for such soft memory signals with future space-based laser interferometers. As realistic examples, we examine the infrared spectral features of gravitational waves from moderately relativistic nonspinning compact binary scattering and comparable-mass quasi-circular, nonprecessing black hole mergers. In both cases, the low-frequency spectrum can be described by a soft displacement-memory waveform with finite-frequency corrections. Using the adopted instrumental-noise models, simulated Bayesian parameter-estimation analyses show that a single LISA-like detector can constrain the memory amplitude and arrival time for signals with matched-filter signal-to-noise ratios of order 10. BBO Stage 1 could measure null displacement memory from sufficiently loud stellar-mass compact binary mergers. We also evaluate the detectability of an idealized stochastic background of soft displacement-memory signals. These results establish gravitational-wave bursts with memory as concrete targets for space-based interferometers.

arXiv comment35 pages, 28 figures; accepted for publication in Physical Review D