Early Warnings of Binary Neutron Star Coalescence Using the SPIIR Search

Gravitational waves from binary neutron star mergers can be used as alerts to enable prompt follow-up observations. In particular, capturing prompt electromagnetic and astroparticle emissions from the moment of a binary merger presents unique constraints on the timescale and sky localization for online gravitational-wave detection. Here we present the expected performance of the SPIIR online detection pipeline that is designed for this purpose in the upcoming international LIGO–Virgo's 4th Science Run (O4). Using simulated Gaussian data for the two LIGO observatories with expected O4 sensitivity, we demonstrate that there is a nonnegligible opportunity to deliver premerger warnings at least 10 s before the final plunge. These alerts are expected to be issued at a nominal rate of one binary neutron star coalescence per year and localized within a median searched area of 300 deg2. We envision such detection to be extremely useful for follow-up observatories with a large field of view such as the Murchison Widefield Array radio facility in Western Australia.