Gravitational-wave Merger Forecasting: Scenarios for the Early Detection and Localization of Compact-binary Mergers with Ground-based Observatories

We present the prospects for the early (pre-merger) detection and localization of compact-binary coalescences using gravitational waves over the next 10 yr. Early warning can enable the direct observation of the prompt and early electromagnetic emission of a neutron star merger. We examine the capabilities of the ground-based detectors at their "Design" sensitivity (2021–2022), the planned "A+" upgrade (2024–2026), and the envisioned "Voyager" concept (late 2020s). We find that for a fiducial rate of binary neutron star mergers of 1000 Gpc−3 yr−1, the Design, A+, and Voyager era networks can provide 18, 54, and 195 s of warning for one source per year of observing, respectively, with a sky localization area <100 deg2 at a 90% credible level. At the same rate, the A+ and Voyager era networks will be able to provide 9 and 43 s of warning, respectively, for a source with <10 deg2 localization area. We compare the idealized search sensitivity to that achieved by the PyCBC Live search tuned for pre-merger detection. The gravitational-wave community will be prepared to produce pre-merger alerts. Our results motivate the operation of observatories with wide fields of view, automation, and the capability for fast slewing to observe simultaneously with the gravitational-wave network.