Expanding Horizons - Transforming Astronomy in the 2040s Time-Domain Multi-Messenger Astronomy in the 2040s: EM Follow-up of LGWA Sources

TL;DR

The paper discusses how the Lunar Gravitational Wave Antenna (LGWA) will open a new gravitational-wave detection window in the 2040s, enabling predictive EM follow-up of compact binaries before merger, transforming multi-messenger astronomy.

Contribution

It identifies the scientific opportunities enabled by LGWA and highlights the need for new EM observational capabilities in the 2040s.

Findings

LGWA will detect compact binaries months to years before merger.

Predictive EM follow-up will revolutionize understanding of merger environments.

New ground-based EM facilities are needed for rapid, wide-area follow-up.

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.