"It's amazing — we've been waiting for a flash this bright from a gamma-ray burst ever since Swift began observing the sky three years ago, and now we've got one that is so bright that it was visible to the naked eye even though its source is half-way across the universe," said David Burrows of Penn State University, who directs the continuing operation of Swift's X-ray telescope and the analysis of the data it collects.

Gamma-ray bursts are the most luminous explosions in the universe since the Big Bang and occur when massive stars run out of nuclear fuel. The stars' cores collapse to form black holes or neutron stars and release an intense burst of high-energy gamma-rays and jets of energetic particles.