A gamma-ray burst (GRB) is through to be produced by the explosion of a massive star (i.e. a supernova). This explosion produces high energy gamma-ray photons that travel easily through the universe, unhindered by the dust and gas that attenuates optical photons. Upon reaching Earth, these gamma-ray photons are detected by one of several GRB satellites in orbit (including HETE-2, INTEGRAL and SWIFT).

These detection events only last for a few seconds or a few tens of seconds but by calculating the direction from which these photons arrive a GRB satellite can quickly determine the approximate coordinates (RA and DEC) of the GRB. From the detection of gamma-rays alone, however, GRBs can only be localized - at best - to within a radius of a few arcminutes. Such a rough localization does not allow the host galaxy of a GRB to be uniquely identified.

Fortunately, the initial burst of gamma-ray photons is followed by a flux of lower energy photons at X-ray, optical, IR and radio wavelengths. These photons are called the GRB's "afterglow" (AG). The AG light may initially be very bright but will dim steadily over time. In order to detect AG, therefore, it is important to begin observations as soon as possible after a GRB alert is issued. Not every GRB produces a detectable optical or IR AG, however, possibly because the AG photons are scattered by dust.

If an AG is detected at X-ray, optical, IR or radio wavelengths then the GRB can be localized to within a few arcseconds, so that the host galaxy (if visible) may be identified.

Even if no afterglow is observed, multiple images are taken of the GRB's coordinates in the days and weeks that follow so that any supernova brightening that is associated with the GRB can be identified.