| Abstract : | The pre-merger (early-warning) gravitational-wave (GW) detection and localization of a compact binary merger would enable astronomers to capture potential electromagnetic (EM) emissions around the time of the merger, thus shedding light on the complex physics of the merger. While early detection and localization are of primary importance to the multimessenger follow-up of the event, improved estimates of luminosity distance and orbital inclination could also provide insights about the observability of the EM transients from the source. In this work, we demonstrate that the inclusion of higher modes of gravitational radiation, which vibrate at higher multiples of the orbital frequency than the dominant mode, would significantly improve the estimates of the luminosity distance and orbital inclination of the binary, in early-warning time, thus enabling astronomers to better determine their follow-up strategy. Focusing on future observing runs of the ground-based GW detector network (O5 run of LIGO-Virgo-KAGRA, Voyager, and third-generation (3G) detectors), we show that for a range of masses spanning the neutron-star black-hole regime that are potentially EM-bright, the inclusion of higher modes provides improvements in luminosity distance error bars by factors as large as ∼ 1.4 − 20(1 − 10) for the O5 and Voyager (3G) observing scenario 45 (300) seconds before the merger for the sources located at 100 Mpc, with significant improvements in orbital inclination estimates as well. We also investigate these improvements for a range of luminosity distances and inclination angles as well as with varying sky-location and polarization angle. Combining the luminosity distance uncertainties with localization skyarea estimates, we find that the number of galaxies within the error volume that might have hosted the merger, is reduced by a factor of ∼ 1.5 − 100(1.8 − 100) [1.2 − 20] with the inclusion of higher modes at early-warning time of 45 (45)[300] seconds in O5 (Voyager)[3G] scenario. |
