Sankey diagram showing the outcome of real-time alerts and the provenance of astrophysical GW events during LIGO and Virgo’s third observing run, using data from the Gravitational-Wave Candidate Event Database (https://gracedb.ligo.org/superevents/public/O3/) and the Gravitational Wave Open Science Center (https://gwosc.org/eventapi/html/query/show?min-gps-time=1230336018&lastver=true). Compact binary coalescence alerts are labeled by their highest probability source classification. Events with data-quality issues identified in real time are labeled as “retracted.” Events with a probability of astrophysical origin p _astro < 50% after further analysis are labeled as “marginal.” Events with a false-alarm rate of FAR > 2 yr⁻¹ after further analysis are not included in the final catalog (LIGO Scientific Collaboration & Virgo Collaboration 2021a; LIGO Scientific Collaboration et al. 2023). Only three confirmed and two marginal events containing an NS had alerts allowing follow-up in real time. SAGUARO covered a portion of the localization region for four of these events and discovered a single possible counterpart, which was unlikely to be a kilonova based on its luminosity (Paterson et al. 2021). An interactive version of this figure that includes counts and event names for each flow is available.

An interactive version of this figure is available in the online journal.