X-ray and Observational Astronomy

News April 2002: XMM observation of gamma ray burst shows supernova connection

The XMM-Newton EPIC X-ray image of the afterglow, taken 11 hours after the gamma ray burst	The early XMM-Newton spectrum of the 11th Dec 2001 gamma ray burst afterglow, showing the shifted emission lines	An R-band VLT image taken by Ingunn Burud (STScI) of the optical transient and its host galaxy

An observation by XMM-Newton of the gamma ray burst GRB011211 started 11 hours after the burst revealed a fading X-ray source. The big news is that in the first hours of this observation strong emission lines due to light elements were seen for the first time in a gamma ray burst afterglow. Previous reports have only identified emission from Iron.

These emission lines are blue-shifted with respect to the host galaxy, indicating a shell of hot gas expanding at 0.1c. This is another new discovery for gamma ray burst afterglows, and strongly suggests that the burst was preceded a few days earlier by a supernova explosion.

This idea is consistent with 'collapsar' or 'hypernova' models of gamma ray bursts, in which a massive star (greater than around 10 solar masses) collapses under its own weight when its nuclear fuel is exhausted. If such a massive star were rotating (as seems most likely), then it would collapse to a black hole, but only after an interval of rotational support. Along the rotation axes, the stellar matter is unsupported, collapsing into the black hole and forming highly relativistic jets which are the origin of the gamma rays. (MacFadyern & Woosley 1999, ApJ 524,262).

This new clear association of a gamma ray burst with a supernova is published by Reeves et al in Nature (April 4, 2002). The Nature paper authors are from the University of Leicester: James Reeves, Darrach Watson, Julian Osborne, Ken Pounds, Paul O'Brien, Alex Short, Martin Turner & Mike Watson; from University College, London: Keith Mason; and from the European Space Agency in Villafranca, Spain: Mathias Ehle and Norbert Schartel. A PPARC press release and an ESA press release, and the paper itself (as .pdf and .ps files) are all available.

The XMM-Newton EPIC camera used to obtain this result was built by a team led by Dr Martin Turner of the University of Leicester. A similar camera will be carried by the NASA satellite Swift, due to be launched in the autumn of 2003. Swift will detect 2 or 3 new gamma ray bursts each week, rapidly maneuvering to point its X-ray and optical telescopes at the burst and afterglow within 20 seconds. This satellite has the capability to revolutionise gamma ray burst research.

Other news items are available here.

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Last updated: 2002 April 5 by Julian Osborne