A
gamma ray burst, as the name suggests, is a huge amount of
gamma radiation released in
space, that contains roughly the same amount of
energy as a
supernova. Unlike
supernovae however, the energy in a gamma ray burst is released in a matter of
seconds (between 30ms-1000s) as opposed to
days,
weeks or even
months as the case may be with the former.
They are detected with two types of telescope, one to closely examine an area of the sky, not unlike a wide angle lens on a camera, and another to focus the x-rays onto a sensor. The sensor is hooked up a computer equipped with sophisticated artificial intelligence software that can pick out the extragalactic bursts of energy faster than any human could by hand.
When looked at in terms of matter and energy, imagine that the amount of material it takes to create a 1 megaton nuclear explosion could fit into a coffee jar. Now imagine the size of the explosion if instead of a coffee jar's worth of material, you had an entire star's worth. Now you're in the ball park.
Gamma ray bursts were first discovered by satellite detectors in the sixties. When these strange busts of radiation were discovered, government scientists thought that the Soviet military were conducting clandestine nuclear tests, or that the bursts might be emissions from some alien spacecraft. It was only later when it was discovered that the bursts originated deep in outer space that the information was declassified and made available to the public.
The bursts are not limited to one particular part of outer space, but occur randomly and without pattern. The one thing they do have in common is that nobody knows for sure what causes them.