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Abstract

Accurate models of gravitational waves from merging binary black holes are
crucial for detectors to measure events and extract new science. One important
feature that is currently missing from the Simulating eXtreme Spacetimes (SXS)
Collaboration's catalog of waveforms for merging black holes, and other
waveform catalogs, is the gravitational memory effect: a persistent, physical
change to spacetime that is induced by the passage of transient radiation. We
find, however, that by exploiting the Bondi-Metzner-Sachs (BMS) balance laws,
which come from the extended BMS transformations, we can correct the strain
waveforms in the SXS catalog to include the missing displacement memory. Our
results show that these corrected waveforms satisfy the BMS balance laws to a
much higher degree of accuracy. Furthermore, we find that these corrected
strain waveforms coincide especially well with the waveforms obtained from
Cauchy-characteristic extraction (CCE) that already exhibit memory effects.
These corrected strain waveforms also evade the transient junk effects that are
currently present in CCE waveforms. Lastly, we make our code for computing
these contributions to the BMS balance laws and memory publicly available as a
part of the python package $\texttt{sxs}$, thus enabling anyone to evaluate the
expected memory effects and violation of the BMS balance laws.