Some now and then it is possible to catch a flash of energetic gamma rays that can last from seconds to hours and happen about once per day in random positions in the sky. They are known as gamma ray bursts (GRB) and were found in the 60's when satellites were looking for gamma ray pulses from nuclear weapons on Earth. Since then many dedicated satellites were launched to study them. There are proposals to explain some of mass extinction on Earth as being due to a nearby GRB.
There are two categories of GRB: the short bursts and the long ones which last for more than two seconds. It seems that there is a consensus about the origin of the long bursts but the situation for the short duration bursts is still inconclusive. A good review on GRB can be found in the Wikipedia.
Now a team of astronomers are proposing a
new class of intermediate bursts after a GRB that was detected in January 2006. It looks like a short GRB but it seems to be too far away. If they are right the amount of energy released is incredible high. GRB are important because they may need new physics for a full understanding of its properties.