localization

The term localization (or sky localization) has been used in regarding transient detection, for characterizations of the region of the sky within which the transient is known to have occurred (a precise location within the sky may not be evident), and also for the process of narrowing this region. Various measures are sometimes used to quantify localization, such as a specific area of the sky, or a probability density function (PDF) over the sky. The term has been used regarding GW detections, and definitely applies to other transients such as gamma-ray bursts, X-ray flashes, fast radio bursts, and neutrino and cosmic-ray detections. PDF information is offered by the directionality of antennas or other detectors, and additional information is available from precise timing of detections of the same event by multiple detectors, as well as the relative signal strength of detectors that have some directionality and are oriented differently. For example, the two LIGO gravitational-wave detectors and the Virgo Detector have different attitudes, all being oriented along the ground on which they stand, and the Virgo detector's sensitivity differs from that of the LIGO detectors. The timing of detected gravitational waves, as well as the indicated strength allows determination of a likely portion of the sky from which the signal arrived, assisting in searches for counterparts.