Estimating Event Rates for Orphaned Memory in LISA

A key prediction of General Relativity is nonlinear memory, but it has yet to be physically observed. The gravitational waves from accelerating masses—such as merging black holes—should produce permanent distortions in spacetime that are potentially detectable by future space-based detectors like the Laser Interferometer Space Antenna (LISA). If the inspiral of two distant massive black holes is detected by LISA, the subsequent merger might be too high in frequency or too low in amplitude to be directly observed. However, it can still be spectrally forecasted, which would enable the prediction of the associated memory burst, even if the merger itself is beyond LISA's sensitivity curve. When memory is seen without a 'parent' merger, it is considered 'orphaned'. We update the orphan memory event rates for LISA by making random draws from population distributions. The population data is updated from previous work to include sources of lower mass and greater comoving distance. For greater accuracy, we also include the oscillatory component using the GWSurrogate waveform package rather than implementing the semi-analytic step-function approximation typically made for nonlinear memory. We then pass our waveform through the LISA response function, transform it into the characteristic strain, and compare it with the LISA sensitivity curve. In this talk, we present the preliminary expectations of orphan memory detectability over LISA's 4-year mission and discuss implications for future multi-messenger astrophysics.