Editor's Summary
13 July 2006
First lights
When a bright 
-ray burst is sighted, two distinct types of optical emission are seen during the first few minutes after the burst: the 'prompt' emission and the early afterglow. GRB 050820a, a burst that occurred on 20 August last year, provided astronomers with the opportunity to answer the question: "when does the early afterglow begin?" The answer: not at the burst trigger time as is normally assumed. Rather, it seems to be a response or reverberation related to the energy release measured by the prompt optical and -ray emission. This opens a new area of -ray burst research because the response to the impulse energy can be used to probe the properties of the jet and the surrounding medium.
Letter: Energy input and response from prompt and early optical afterglow emission in 
-ray bursts
W. T. Vestrand, J. A. Wren, P. R. Wozniak, R. Aptekar, S. Golentskii, V. Pal'shin, T. Sakamoto, R. R. White, S. Evans, D. Casperson and E. Fenimore
doi:10.1038/nature04913