Multi-messenger detections of binary neutron star mergers powered by decihertz gravitational-wave observations

As the only binary neutron star (BNS) merger detected thus far via both gravitational waves (GWs) and definitive electromagnetic (EM) counterparts, GW170817 not only provided crucial information for many astrophysical processes but also opened an exciting era of multi-messenger astronomy. However, due to the high operating frequency, ground-based GW detectors cannot provide alerts with a sufficient early-warning time, making it difficult for EM facilities to capture the early evolution of detectable BNS mergers. In view of this, we assess the detections and early-warning abilities of space-borne decihertz GW detectors for BNS mergers because they can provide alerts much earlier. We discuss the precision in localization and timing for two proposed decihertz GW observatories, B-DECIGO and DO-Conservative, as an extension of recent work. During an assumed 4-year mission time, sources that merge in 1–4 years will yield the most precise angular resolution with ΔΩ~10 –2 deg 2 and time-of-merger accuracy with Δ t c ~0.2 s. After BNS mergers, we examine the possibility of multi-messenger early-warning detections with space-borne decihertz GW detectors for different types of EM transients, covering γ-ray/X-ray to radio bands. Based on our analyses, we propose that a “wait-for” detection scheme could open up new opportunities for future multi-messenger astronomy.