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Abstract

We present the prospects for the early (pre-merger) detection and
localization of compact-binary coalescences using gravitational waves over the
next 10 years. 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 2020's). We find that for a fiducial rate of binary neutron star
mergers of $1000 ~\mathrm{Gpc}^{-3} \mathrm{yr}^{-1}$, the Design, A+, and
Voyager era networks can provide 18, 54, and 195s of warning for one source per
year of observing, respectively, with a sky localization area $<$100 deg$^2$ at
a $90\%$ credible level. At the same rate, the A+ and Voyager era networks will
be able to provide 9 and 43s of warning, respectively, for a source with $<$10
deg$^2$ 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.