Follow-Up & Data Products

The race to find the electromagnetic counterpart of a gravitational-wave event — wide-field telescopes tiling the large localization region, imaging it repeatedly to catch the one new point of light that is the merger's afterglow among millions of unrelated sources.

Working out where on the sky a gravitational-wave source lies, from the tiny differences in when and how strongly each detector in the network registers the wave. With only two or three detectors the region can be huge — hundreds of square degrees — which is what makes the counterpart search so hard.

The time-critical mobilisation of telescopes within minutes to hours of a gravitational-wave alert. A kilonova fades in days and the earliest light carries the most information, so automated systems and rapid human decisions decide whether the counterpart is caught at all.

The signal itself — the rising chirp of a compact binary as it spirals in, merges, and rings down. Matching the observed waveform against banks of theoretical templates is how a real signal is dug out of the detector noise and how its source is identified.

The cumulative catalogue of confident gravitational-wave detections from the LIGO–Virgo–KAGRA observing runs — the growing census of compact-binary mergers, released as open data, from which the population of black holes and neutron stars across cosmic time is reconstructed.

Inferring the properties of a gravitational-wave source — the masses and spins of the merging objects, the distance, the orientation — by comparing the waveform against models. It is how a chirp becomes a measurement, including the standard-siren distance that probes the expansion of the universe.

The probability map of where a gravitational-wave source lies on the sky, released with each alert. Rather than a single point it is a spread of probability — often a long banana-shaped arc — that observers use to plan which patches of sky to search first.