Gamma ray bursts (GRB) are short flashes of light, characterized the high energy gamma ray photons that are detected. The above image is an artist's conception of a gamma ray burst. GRB signals have high redshifts, so they must be signals from very faraway events. Also, the signal can change rapidly, so it must be coming from a relatively small source. The light coming from a GRB is so intense that we theorize that it must be beamed jets from a very high energy explosion. If light this powerful was shining out in every direction, such an explosion would be way too powerful to be physical, with hundreds of times more energy than a typical supernova being produced in a matter of seconds. GRB's can last anywhere from a few milliseconds to a few hours. When they shine, they are the brightest objects in the universe.
This animation depicts the merger of two neutron stars, resulting in a short gamma ray burst. The actual merger would only take a few milliseconds, and the afterglow of an event like this one would be very short, since there is not much surrounding material to sustain it.
This simulation depicts the gravity waves produced by two neutron stars orbiting a common center of mass. Gravity waves carry off energy. Over time, this loss of energy causes them to spiral inward toward each other and eventually merge. The merger is very energetic and produces gamma ray photons in a short burst.
This video depicts a gamma ray burst being created by a core collapse supernova. Not all core-collapse supernovae produce gamma ray bursts, but if the geometry of the event causes the energy of the explosion to be channeled out in beams, the confined light is very much brighter than it would be if it was shining out in every direction, much like a laser beam, as compared to a light bulb.
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This map shows locations in the sky where gamma ray bursts have been detected. It is a map of the whole sky. On a map like this, the plane of the Milky Way lies along the x-axis. The fact that gamma ray bursts have been detected everywhere in the sky means that they are not coming from just our own galaxy, they must becoming from the universe as a whole.