The optical afterglow of the short γ-ray burst GRB 050709


It has long been known that there are two classes1 of γ-ray bursts (GRBs), mainly distinguished by their durations. The breakthrough in our understanding of long-duration GRBs (those lasting more than 2 s), which ultimately linked them with energetic type Ic supernovae2,3,4, came from the discovery of their long-lived X-ray5 and optical6,7 ‘afterglows’, when precise and rapid localizations of the sources could finally be obtained. X-ray localizations have recently become available8,9 for short (duration <2 s) GRBs, which have evaded optical detection for more than 30 years. Here we report the first discovery of transient optical emission (R-band magnitude 23) associated with a short burst: GRB 050709. The optical afterglow was localized with subarcsecond accuracy, and lies in the outskirts of a blue dwarf galaxy. The optical and X-ray10 afterglow properties 34 h after the GRB are reminiscent of the afterglows of long GRBs, which are attributable to synchrotron emission from ultrarelativistic ejecta. We did not, however, detect a supernova, as found in most nearby long GRB afterglows, which suggests a different origin for the short GRBs.

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Figure 1: The classic BATSE duration–spectral hardness diagram1.
Figure 2: The optical afterglow of GRB 050709.
Figure 3: Light curve of the optical counterpart to GRB 050709.


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We thank T. Tauris for discussions. The Dark Cosmology Centre is funded by the DNRF. We acknowledge benefits from collaboration within the EU FP5 Research Training Network ‘Gamma-ray bursts: an enigma and a tool’.

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Hjorth, J., Watson, D., Fynbo, J. et al. The optical afterglow of the short γ-ray burst GRB 050709. Nature 437, 859–861 (2005).

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