Astrophys. J. 720, 1008–1015 (2010)

Gamma-ray bursts are flashes of extremely high-energy gamma rays, thought to be caused by the merger of neutron stars or the death of massive stars. Alessandra Corsi, currently at the California Institute of Technology in Pasadena, and her colleagues tried to tease out the details of the fireball explosion that produces the signal by analysing one short gamma-ray burst: GRB 090510, which was observed by NASA's Fermi Gamma-r Ray Space Telescope, and other satellites, in May 2009.

The authors say that a simple model, in which all of the signal is due to radiation from particles accelerated by shockwaves, cannot explain the fact that the signal starts off at lower energy and then moves to higher energy. Instead, they suggest a twofold mechanism, with the initial signal coming from emissions from particles accelerated in a first shell around the fireball's centre, and the remainder from particles in a second, faster-moving shell.