The afterglow of GRB 050709 and the nature of the short-hard γ-ray bursts


The final chapter in the long-standing mystery of the γ-ray bursts (GRBs) centres on the origin of the short-hard class of bursts, which are suspected on theoretical grounds to result from the coalescence of neutron-star or black-hole binary systems. Numerous searches for the afterglows of short-hard bursts have been made, galvanized by the revolution in our understanding of long-duration GRBs that followed the discovery in 1997 of their broadband (X-ray, optical and radio) afterglow emission. Here we present the discovery of the X-ray afterglow of a short-hard burst, GRB 050709, whose accurate position allows us to associate it unambiguously with a star-forming galaxy at redshift z = 0.160, and whose optical lightcurve definitively excludes a supernova association. Together with results from three other recent short-hard bursts, this suggests that short-hard bursts release much less energy than the long-duration GRBs. Models requiring young stellar populations, such as magnetars and collapsars, are ruled out, while coalescing degenerate binaries remain the most promising progenitor candidates.

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Figure 1: HST and Chandra X-ray Observatory images of the afterglow and environs of GRB 050709.
Figure 2: Spectrum of the host galaxy of GRB 050709.
Figure 3: Observations of the GRB 050709 afterglow and illustrative models.
Figure 4: Physical properties of the afterglows of long-duration GRBs (histograms) and SHBs (arrows).


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Our GRB research is supported in part by funds from NSF, NASA, the Australian Research Council, and the Ministry of Education, Science, Culture, Sports, and Technology in Japan. The VLA is operated by the National Radio Astronomy Observatory, a facility of the NSF operated under cooperative agreement by Associated Universities, Inc. The Gemini Observatory is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership. This work is based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

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Correspondence to D. B. Fox or D. A. Frail.

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Fox, D., Frail, D., Price, P. et al. The afterglow of GRB 050709 and the nature of the short-hard γ-ray bursts. Nature 437, 845–850 (2005).

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