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 (given that a precise location within the sky may not be evident), and also for the process of narrowing this region. This is relevant because some means of detecting transients do not provide precise information regarding where the transient occurred; example such detectors are gravitational-wave detectors, neutrino observatories, cosmic-ray detectors, X-ray flash detectors, gamma-ray burst detectors, and fast radio burst detectors. (While detection methods are constantly improving regarding providing some precision, methods of detection have varied widely in this capability, even to the extent of providing no directionality whatsoever.) 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. 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 GW 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 precise timing-differences of the detections of a gravitational wave event, as well as each's indicated strength allows determination of a likely portion of the sky from which the signal arrived, assisting in searches for counterparts.