Probing Gamma-ray Bursts and their Progenitors with Multiwavelength Observations

California Institute Of Technology, Pasadena CA

Investigators

Abstract

AST 0098676 Kulkarni Cosmic gamma-ray bursts (GRBs) are among the most spectacular, known phenomena in the universe. They consist of short outbursts (fractions of seconds to a few minutes) of high-energy radiation originating in distant regions of the universe, There are a few such outbursts observed per day. These were first observed by the US Vela satellites in the early 1960's. They have remained one of the major mysteries of astrophysics for the past 30 years. In the late 1990's breakthrough discoveries found that the bursts originated in faint galaxies, at typical distances of several billion light years. Measurements of distances to the bursts, using large, ground-based telescopes, revealed that apparently some of them emit prodigious amounts of energy; larger than the total amount of energy produced by our Sun over its entire projected lifespan of about 10 billion years, but compressed into a few seconds! While theories abound, the ultimate cause of these amazing cosmic explosions remains unknown. However, it now seems likely that at least some bursts represent "birth cries" of black holes, produced in the explosion of massive stars ("hypernovas"). Current research suggests that the GRB phenomenon is closely related to the history of star formation in the universe, and that it can be used as a novel probe of early cosmic evolution. It is also likely that most GRBs produce highly collimated jets of very energetic particles and radiation, effectively becoming giant accelerators in the sky. While a lot has been learned over the past few years, much more remains to be found about the source and the ultimate physical mechanism behind these remarkable cosmic explosions. The keys to this further understanding lies in (1) detailed observations of their afterglows seen at wavelengths ranging from radio waves, through visible light and out to x-rays; (2) additional measurements of the distances to these enigmatic events; and (3) a better understanding of their environments and the distant galaxies in which they originate. This is the subject of the present project. Using the worlds largest optical/infrared telescopes (the 10-m Keck telescopes in Hawaii and the large telescopes at Mt. Palomar in California), and the world's premier radio telescopes (e.g., the Very Large Array in New Mexico) to observe GRBs when they are first identified and to continue to observe them as they decline in brightness, the goal is to construct a wide enough bank of data to permit testing and winnowing of the scores of theoretical models presently under study. Funding for this project was provided by the NSF program for Extragalactic Astronomy & Cosmology (AST/EXC). ***