Search for nonlinear memory from subsolar mass compact binary mergers

We present the first results of the search for nonlinear memory from subsolar mass binary black hole (BBH) mergers during the second observing run (O2) of the LIGO and Virgo detectors. The oscillatory chirp signal from the inspiral and merger of low mass BBHs (Mₓ₎ₓ0. 4 M_) are at very high frequencies and fall outside the sensitivity band of the current ground-based detectors. However, the nonoscillatory memory signal during the merger saturates toward the lower frequencies and can be detected for those proposed BBHs. We show in this work that the morphology of the memory signal depends minimally upon the source parameters of the binary, thus only the overall amplitude of the signal changes and hence the result can be interpolated for extremely low mass BBH mergers. We did not find any signal which can be interpreted as a memory signal, and we place upper limits on the rate of BBH mergers with Mₓ₎ₓ0. 4 M_ for the first time.