Mysterious gamma-ray bursts
About twice a day satellites in orbit register a burst of gamma-rays somewhere in the Universe. These bursts may last a hundredth of a second, or anything up to 90 minutes. Some bursts become briefly the brightest objects in the gamma-ray sky. For over twenty years the astronomers hadn't a clue as to how far away these explosions occurred until in early 1997 the Italian-Dutch satellite Beppo-SAX provided accurate X-ray measurements that allowed to pinpoint the position of a burst and enabled follow-up observations with optical and other telescopes.
The observations at different wavelengths confirmed that the gamma-ray bursts are extremely distant and therefore must be caused by tremendous explosions. On 23 January 1999 there was another exciting event. Using orbiting observatories and ground-based telescopes, astronomers from all over the world tracked the visible glow of a gamma-ray burst while it was still emitting high-energy radiation. They discovered that this burst was the most energetic eruption ever recorded, equal to the radiance of one million galaxies or 100 million billion stars.
Where does this unbelievable amount of energy come from? Astronomers don't have an answer yet. Maybe gamma-ray bursts are created by the mergers of a pair of neutron stars or black holes, or by a hypernova, a theorized type of exceptionally violent exploding star. Better observations are necessary to solve the riddle. With Integral gamma-ray bursts will be studied using the very broad energy range provided by the two main instruments and the X-ray and optical monitors.