University of Leicester eBulletin

Astronomers unravel mystery of gamma ray bursts

April 2002

No 74

XXM telescope MISSION POSSIBLE: Scientists from the Department of Physics and Astronomy contributed to the development of the X-ray Multi-Mirror [XMM]-Newton telescope, the biggest and most sensitive X-ray telescope ever to be placed in to orbit, which is able to study extremely faint X-ray sources from stars and galaxies in the most distant parts of the Universe

The cause of gamma ray bursts, the most violent and explosive events in the Universe, has remained a mystery since they were first discovered in 1967. Now a team of scientists, led by astronomers from the University of Leicester, believes they have found an answer to the puzzle. Their research results [published in Nature on 4th April] indicate that gamma ray bursts are caused by the death of a star so huge that when it dies in a supernova, its core collapses to form a black hole, resulting in an intense outburst of gamma rays.

Dr Julian Osborne of the University of Leicester explained: “Until now it was unclear whether gamma ray bursts were caused by a supernova explosion of a giant star collapsing into a black hole, or by the coalescence of two neutron stars.  Each event could result in an intense outburst of gamma rays, followed by an X-ray afterglow. By analysing this X-ray afterglow we believe we have determined the gamma ray burst origin.”

The scientists used the EPIC (European Photon Imaging Camera) instrument on the European Space Agency's [ESA] XMM-Newton space telescope to capture the X-ray afterglow of a recent gamma ray explosion in a galaxy 10 billion light years from Earth, and then conducted a detailed spectral analysis of the data. The results were a great surprise.

Dr James Reeves of the University of Leicester added: “For the first time ever traces of light chemical elements were detected - including magnesium, silicon, sulphur, argon, and calcium - neutron star collisions are not expected to make these. Also, the hot cloud containing these elements is moving towards us at one tenth of the speed of light. This suggests that the gamma ray burst resulted from the collapse of the core of a giant star following a supernova explosion. This is the only way the light elements seen by XMM-Newton, speeding away from the core, could be produced. So the source of the gamma ray burst is a supernova and not a neutron star collision.”

He added: “The confirmation by XMM-Newton that gamma ray bursts are associated with supernovae therefore brings scientists closer to understanding the process that leads to the burst itself.”

The UK has taken a leading role in XMM-Newton, as Professor Ian Halliday, Chief Executive of the Particle Physics and Astronomy Research Council explains: “From the development of the XMM-Newton concept, the UK has been taking a strong role, with the University of Leicester leading the way on the EPIC instrument and on the Survey Science Centre consortium which processes all the data recorded. The Mullard Space Science Laboratory built the Optical Monitor telescope on XMM-Newton, which also captured the fading optical signature of the gamma ray burst.”

Professor Ian Halliday, adds: “These latest findings will be tested by SWIFT; a NASA led space mission that scientists from the University of Leicester and Mullard Space Science Laboratory are helping to build.  Once it is launched in autumn next year [2003], SWIFT will study over 1000 gamma ray bursts, spotting them rapidly then automatically turning two much more sensitive telescopes to study these events.  This means that the resulting X-rays can be studied mere seconds after the event, instead of the hours presently required to manoeuvre existing space-based telescopes with instructions from the ground.”

Notes for Editors:

Images

Hypernova, XMM, and Swift images are available from the PPARC web site: www.pparc.ac.uk  or by contacting Gill Ormrod at PPARC press office on 01793 442012. Email: gill.ormrod@pparc.ac.uk

Background notes

XMM-Newton
At 3.9 tonnes and 10 metres long, the X-ray Multi-Mirror [XMM]-Newton is the biggest and most sensitive X-ray telescope ever to be placed in to orbit. It is able to study extremely faint X-ray sources from stars and galaxies in the most distant parts of the Universe.

EPIC the European Photon Imaging Camera
This instrument, built by an international team of European scientists led by Dr Martin Turner of the University of Leicester uses silicon Charge Coupled Devices to provide simultaneous X-ray images and spectra so that the chemical composition of distant X-ray sources can be studied.

Gamma ray bursts
Every day, somewhere in the Universe, there is a gamma ray burst; they are the most powerful and violent phenomena in the Universe. Gamma ray bursts last only a minute or so. But in that time the energy released is equivalent to the instantaneous conversion of up to the entire Sun's mass into energy, following Einstein's famous equation E=mc2, making gamma ray bursts second only to the Big Bang in total power.

The intense burst of gamma rays is followed by an X-ray glow that lasts a few days; it is this X-ray afterglow that was observed by XMM-Newton about 11 hours after the gamma ray burst.

Gamma ray bursts were discovered in 1967 by the US Military VELA satellites where they mimicked the signatures of terrestrial nuclear tests. Several thousand have been detected since, although it was only five years ago that they were proven to come from distant galaxies.

Supernova
A supernova is the explosion produced when a massive star ends its life; one occurs in our own Galaxy approximately every hundred years. Seen from the Earth, it would be initially visible in daylight and would be the brightest star in the sky for about six months. Supernovae in distant galaxies appear much fainter, but briefly outshine the host galaxy itself. The chemical elements that make up the Earth, and ultimately ourselves, were formed in supernovae.  

Contact Details:

Peter Barratt , Head of Communications, Particle Physics and Astronomy Research Council : Tel: 01793 442025 , Mobile: 07879 602899 , Email: peter.barratt@pparc.ac.uk

University of Leicester, Department of Physics & Astronomy :
Dr James Reeves, Tel: 0116 2523510, Email: jnr@star.le.ac.uk
Dr Julian Osborne, Tel: 0116 2523598, Email: julo@star.le.ac.uk
Dr Paul O'Brien, Tel: 0116 2525203, Email: pto@star.le.ac.uk

Mullard Space Science Laboratory, University College London:
Professor Keith Mason, Email: kom@mssl.ucl.ac.uk (Not available on April 3rd)
XMM-Newton Project Scientist, ESTEC, Noordwijk, Netherlands
Dr Fred Jansen Tel: 0031 71 5654426, Email: fjansen@rssd.esa.int

NATURE Authors:
J N Reeves, D Watson, J P Osborne, K A Pounds, P T O'Brien, A D T Short, M J L Turner, 
M G Watson, K O Mason, M Ehle & N Schartel

The Particle Physics and Astronomy Research Council (PPARC) is the UK's strategic science investment agency. It funds research, education and public understanding in four areas of science - particle physics, astronomy, cosmology and space science.

PPARC is government funded and provides research grants and studentships to scientists in British universities, gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Laboratory for Particle Physics (CERN), and the European Space Agency. It also contributes money for the UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh and the MERLIN/VLBI National Facility, which includes the Lovell Telescope at Jodrell Bank observatory.

PPARC's Public Understanding of Science and Technology Awards Scheme funds both small local projects and national initiatives aimed at improving public understanding of its areas of science.

[University Home] [Press and Publications] [University Index A-Z][University Search][University Help]
Information supplied by: Barbara Whiteman
Last updated: April 2002
University Administration Web Maintainer

This document has been approved by the head of department or section.