Gamma ray bursts (GRBs) were first detected serendipitously in 1967 by gamma ray detectors aboard the Vela satellites, and were announced by Klebesadel et al. in 1973. Work by Enrico Costa and Gerald J Fishman in the last two decades have demonstrated that GRBs are of cosmological origin, and are the brightest sources known in the universe.

GRBs are intense flashes of gamma rays emanating from cosmic sources lasting for a few seconds to minutes. During the flash, a GRB outshines any stars and any galaxies in the universe. We now know that the sources of GRBs reside in distant galaxies and that they appear so bright because they emit narrow beams of relativistic particles, and those that are observed happen to have these beams directed toward Earth. We also know that there are at least two distinct types of GRBs. The long-duration bursts are associated with rare types of supernova explosions and may be caused by the formation of a black hole at the centre of a collapsing massive star. The short-duration bursts may be caused by the merger of two neutron stars.

Although the physical mechanisms responsible for the GRB phenomena remain uncertain, there is no doubt that the GRB sources manifest some of the most extreme physical environments in the cosmos. The ongoing study of GRBs is one of the most exciting fields of astrophysics today.

Gerald J Fishman was Principal Investigator of the BATSE experiment (Burst and Transient Source Experiment), a cluster of gamma ray detectors aboard the Compton Gamma Ray Observatory (CGRO), which operated from 1991 until 2000. The BATSE experiment detected thousands of GRBs and showed that their distribution was nearly uniform in the sky. That result was strong evidence that the sources of GRBs are located at cosmological distances, far beyond the Milky Way galaxy. The BATSE experiment also showed that there are two distinct classes of GRBs.

Enrico Costa led the development of the Dutch – Italian satellite BeppoSAX, which was launched in 1996 and operated until 2002. An X-ray camera aboard BeppoSAX measured accurate positions of the X-ray afterglows of GRBs that enabled observers using ground-based optical telescopes to make the first identification of a GRB with a distant galaxy and the first identification of a GRB with a supernova explosion, confirming their cosmological origin.

For these outstanding achievements, Enrico Costa and Gerald J Fishman are awarded the 2011 Shaw Prize in Astronomy.

Astronomy Selection Committee
The Shaw Prize

7 June 2011  Hong Kong