Expanding Horizons - Transforming Astronomy in the 2040s Time-Domain Multi-Messenger Astronomy in the 2040s: EM Follow-up of LGWA Sources
F. Patat, S. Piranomonte, S. Benetti, A. Bonforte, R. Della Ceca, G. Di Rico, A. Frigeri, J. Harms, M. Olivieri, A. Perali, P. Severgnini, A. Stallone, the LGWA Collaboration
TL;DR
The paper argues that the decihertz GW window opened by the Lunar Gravitational Wave Antenna (LGWA) will enable long-term, pre-merger observations of compact binaries and predictive electromagnetic follow-up, fundamentally transforming time-domain multi-messenger astronomy. It outlines key science cases across pre-merger EM evolution, host-galaxy environments, exotic binary populations, lensing-wide GW events, and Type Ia supernova progenitors, while identifying substantial gaps in current EM capabilities required to exploit these discoveries by the 2040s. The work emphasizes the need for rapid, multiplexed spectroscopy, wide-field high-cadence optical/NIR imaging, and robust data-handling and trigger-integration architectures to coordinate large numbers of candidates per event. Collectively, these insights map out the essential technology, infrastructure, and observational strategies needed to capitalize on LGWA findings and push forward predictive, multi-messenger astronomy into the 2040s.
Abstract
The coming decades will see gravitational-wave (GW) astronomy expand decisively into the mHz-Hz frequency range, opening access to a population of compact binaries that are currently invisible or only detectable moments before merger. The Lunar Gravitational Wave Antenna (LGWA) concept is designed to probe this gap, enabling continuous observation of compact binaries over months to years prior to coalescence, and detecting sources inaccessible to both space-based mHz detectors and current ground-based >10 Hz facilities. This new GW window fundamentally alters the landscape of time-domain multi-messenger astronomy. Rather than reacting to mergers after the fact, LGWA enables predictive, scheduled electromagnetic (EM) follow-up, transforming how compact-object mergers, their environments, and their astrophysical channels are studied. However, fully exploiting LGWA discoveries requires EM capabilities that do not exist today and are unlikely to be available by the 2030s, particularly for wide-area, rapid, spectroscopically rich follow-up at optical and near-infrared wavelengths. This White Paper identifies the key science cases enabled by LGWA that motivate new ground-based capabilities in the 2040s.