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New Rosetta stone for GRBs as supernovae
Posted: 14 April

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A gamma-ray burst (GRB) has been seen exploding at the same time and location as a supernova, further cementing the link between these violent phenomena and the destruction of massive stars. The observations of the GRB, observed on 16 March 2010 by NASA’s Swift satellite, were presented today at the Royal Astronomical Society’s National Astronomy Meeting in Glasgow by Rhaana Starling of the University of Leicester.

An artistic impression of a GRB, such as the 16 March blast observed by the Swift spacecraft. Image: Spectrum/NASA and E/PO/Sonoma State University, Aurore Simonnet.

Gamma-ray bursts – powerful blasts of high energy radiation lasting a few minutes – were discovered in the early 1970s, and remained a complete mystery for over two decades mainly because by the time astronomers were able to swing around their telescopes onto them, the afterglow of whatever had caused the explosion had long since faded. However, by 1997 things had developed to the point where the theory that GRBs are the result of the collapse and destruction of the most massive stars, blasting out bipolar jets of gamma rays, could be seriously considered. Since then fast response telescopes have proved the link. However, being able to watch a supernova exploding as a GRB from beginning to end has proven elusive, with only one other example thus far. This triggered the discovery team to contact the eight-metre Gemini South Telescope to follow up the GRB location at optical wavelengths to find a supernova, SN 2010bh, at that location, providing the perfect case study for the death of an extremely massive star in a nearby galaxy.

The GRB, one of four observed by Swift in one day (which is only the second time this has happened, the first time being the day Arthur C Clarke died, 19 March 2008) was characterised as having low energy, ‘soft’ gamma-rays, with a total energy output of 4 x 1049 ergs. Substantial X-ray emission was also detected from a ‘breakout’, when the supernova shock wave cascades through the dense outer envelope of the dying star. An X-ray breakout has only been seen once before, in the case of SN 2006aj. Meanwhile Gemini, the Very Large Telescope and the Hubble Space telescope saw a Type Ic supernova, which is the explosion of a hydrogen poor Wolf–Rayet star (one of the most massive types of star in existence), in what appears to be an interacting galaxy 850 million light years away.

By putting the two sets of observations together, and continuing to monitor the afterglow of the supernova as it fades, it will be possible to compile a complete history of this GRB/supernova, to help better understand the mechanisms that drive these powerful events.