Constraints on Line-of-Sight Acceleration from O1-O4

Abstract: A compact binary will experience a center-of-mass (CoM) acceleration in the vicinity of a massive third object. The line-of-sight (LOS) component of this acceleration is imprinted on gravitational waves produced by the compact binary as a time-varying Doppler shift. The observation of a non-zero LOS acceleration may indicate the binary is in a dense environment, such as an active galactic nucleus (AGN) disk or nuclear star cluster, etc. We measure the LOS acceleration of all compact binaries observed through the first part of the fourth observing run (O1-O4a) of Advanced LIGO and Virgo in addition to select binaries from later observing runs. We introduce a new method to model the LOS acceleration by directly applying the time-varying Doppler shift in the time domain to the signal produced in the binary's frame; this method can be applied to any waveform model including those with higher order modes, eccentricity, and precession. We find the LOS acceleration for all known binaries to date is consistent with zero. We find that the effects of eccentricity and LOS acceleration are partially degenerate as observed in binaries such as GW200105. Current ground-based observatories are sensitive enough to only constrain scenarios that produce high accelerations, e.g $\sim 10^{-2~}(10^{-5})~\textrm{c}/s$ for BBH (BNS) sources, however, next-generation observatories may be able to constrain the accelerations expected in some dense environments.