Bursting Expectations

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Science  12 Mar 2010:
Vol. 327, Issue 5971, pp. 1303
DOI: 10.1126/science.327.5971.1303-c

The gamma-ray burst GRB 090423 is the most distant astronomical object known. Chandra et al. detected its radio afterglow using the Very Large Array radio astronomy observatory. In combination with previous x-ray and infrared measurements, the data imply that the amount of energy released by GRB 090423 and the properties of its afterglow are not sufficiently different from those of less distant gamma-ray bursts to implicate a different type of progenitor star. Thus, even though GRB 090423 occurred only 630 million years after the Big Bang, there is no reason to believe its progenitor star belonged to the initial generation of metal-free stars, which are thought to have been brighter, hotter, and more massive than stars today. Regardless of distance, there is evidence that long-duration gamma-ray bursts occur preferentially in low-metallicity environments, as expected from stellar evolution theory. Using the Keck telescope, Levesque et al. acquired spectra of the host galaxy and explosion site of GRB 020819—an unusual long-duration gamma-ray burst originally detected in 2002, with no optical afterglow—and their data imply that the burst did occur in a high-metallicity environment.

Astrophys. J. 712, L31; L26 (2010).

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