Heads-up for observatories

A network of third-generation gravitational-wave detectors will enable regular electromagnetic observations of post- and pre-merger emission from compact binary coalescences

August 20, 2021

When gravitational-wave detectors localize compact binary coalescences well before they merge, new observations become possible: high-energy and optical telescopes can regulary observe the prompt emission following the merger and also study any pre-merger emission. How often and how early will a network of third generation detectors be able to pull off this feat? An AEI researcher and a colleague from Université Paris-Saclay now have answered this question. Several times each year, the third generation network would be able to pinpoint the sky position to less than some dozens times the sky area of the full Moon. The results strengthen the science case for detectors like the Einstein Telescope and Cosmic Explorer.

Paper abstract

The number of sources detected as a function of time before merger for our fiducial population of 1.4–1.4 M BNS mergers whose rate tracks the star formation and has a local density of 300 Gpc−3 yr −1. Results are shown for various constraints on the localization area (A90) these detected sources later achieve at 5 minutes prior to merger. Multi-hour advance warning of mergers is possible with the Einstein Telescope. Advance warning of sources that will eventually have a precise localization may provide time for other observatories to be brought into observing mode, reschedule observations, or allow for manual human intervention as needed.

We present the prospects for the pre-merger detection and localization of binary neutron star mergers with third-generation gravitational-wave (GW) observatories. We consider a wide variety of GW networks that may be operating in the 2030s and beyond; these networks include up to two Cosmic Explorer (CE) sites, the Einstein Telescope (ET), and continued observation with the existing second-generation ground-based detectors. For a fiducial local merger rate of 300 Gpc−3 yr −1, we find that the ET on its own is able to detect six and two sources per year at 5 and 30 minutes before merger, respectively, while providing a localization of <10 deg2. A single CE would detect but be unable to localize sources on its own. A two-detector CE network, however, would detect 22 and 0.4 mergers per year using the same criteria. A full three-detector network with the operation of dual CEs and the ET would allow for <1 deg2 source localization at 5 minutes before merger for ∼seven sources per year. Given the dramatic increase in localization and detection capabilities, third-generation observatories will enable the regular observation of the prompt emission of mergers by a broad array of observatories including gamma-ray, X-ray, and optical telescopes. Moreover, sub-degree localizations minutes before merger, combined with narrow-field-of-view high-energy telescopes, could strongly constrain the high-energy pre-merger emission models proposed in the last decade.

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