Dr Julian Osborne of the University of Leicester, Dr Alexander Blustin and Dr Massimiliano De Pasquale (both of the Mullard Space Science Laboratory, UCL) will present some of the first results from Swift, a satellite to study gamma-ray bursts, at the RAS National Astronomy Meeting in Birmingham on Tuesday 5th April.
Launched in November last year, Swift has already detected over 20 bursts, including examples of the poorly understood 'short bursts' and 'X-ray flashes', a very long burst, and changes in X-ray emissions shortly after the burst that show the importance of previously unseen physical effects. Swift also saw and measured in detail a bright 'soft gamma repeater' on December 27th 2004. Although not emitted by Swift¿s main target source, gamma-ray bursts, the intense gamma-rays from the repeater were picked up by the satellite's detectors. Soft gamma repeaters have the strongest magnetic fields known and the burst was probably due to massive change in a neutron star's magnetic field. When it went off, this was the brightest object ever seen outside the Solar System.
Gamma-ray bursts are not well understood because they are difficult to study. They are unpredictable, and never occur in the same place twice. The bright gamma-rays disappear within seconds, and the faint afterglow fades away within a few days to weeks. Because their properties are so different from normal stars and galaxies, traditional space- and ground-based observatories are not able to respond easily before the bursts have faded away. Swift is able to detect the bursts and respond to them within seconds, swinging round to point its X-ray and optical telescopes at the afterglow before it fades. Before Swift the early afterglow behaviour was unknown, but the spacecraft is giving scientists a chance to understand the bursts more clearly.
Swift's first few observations in optical wavelengths of gamma-ray bursts have already dramatically altered our understanding of the afterglow phenomenon. The first discovery relates to "dark bursts", which are gamma-ray bursts with no afterglow in visible light. Until the Swift era, the bursts were though to be ¿dark¿ because their optical emission was shielded from view by the burst¿s immediate environment orby the huge amount of gas in the universe in our line of sight to distant bursts. Swift's ability to observe afterglows very soon after the bursts occurs has provided tantalising evidence that the physics of outflows from some gamma-ray bursts may instead be dominated by strong magnetic fields. Swift observations of non-dark gamma-ray bursts have shown rapid, possibly correlated, variability in the optical and X-ray early afterglows.
Even while Swift was being commissioned it was detecting bursts and observing them in detail. The satellite is working perfectly, and all the Swift instruments have been checked out. At a rate of around 100 bursts a year, Swift will revolutionise this field of astronomy.
The session on gamma-ray bursts at the RAS National Astronomy Meeting also includes a talk by Dr Robert Priddey from the University of Hertfordshire, who will be presenting results of a survey to look for evidence of dusty, star-forming galaxies surrounding gamma ray bursts. A team from the University of Hertfordshire used the Submillimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope in Hawaii to detect light emitted by dust near gamma-ray burst sources. Their results question the current understanding of dusty galaxies and gamma-ray bursts.
Dr Andrew Levan will also be presenting results from studies of X-ray flashes. His findings suggest that X-ray flashes are gamma-ray bursts seen off-axis. He will also show that X-ray flashes are not all associated with bright supernovae, unlike most gamma-ray bursts.
NOTES FOR EDITORS
The 2005 RAS National Astronomy Meeting is hosted by the University of Birmingham, and sponsored by the Royal Astronomical and the UK Particle Physics and Astronomy Research Council (PPARC).
The Swift satellite to study gamma-ray bursts was launched on November 20 2004 from Cape Canaveral. Swift is uniquely designed to study gamma-ray bursts. Most observatories take hours to respond to a burst but Swift can be in position to observe it within a few minutes. It is this quick manoeuvrability that earned the satellite its name.
The UK has made major contributions to Swift, with the Mullard Space Science Laboratory (University College, London) providing the UV/optical telescope, and the University of Leicester providing the X-ray camera and other parts of the X-ray telescope. In addition to the contributing groups, there is a strong gamma-ray burst community amongst UK astronomers, with theoreticians at Cambridge, infra-red observers at Hertfordshire, and large robotic telescopes run from Liverpool John Moores.
Swift is a medium-class explorer mission managed by NASA Goddard in Greenbelt, Maryland, for the Science Mission Directorate, Washington. It is a NASA mission with participation of the Italian Space Agency and the Particle Physics and Astronomy Research Council (PPARC) in the United Kingdom. It was built in collaboration with US national laboratories, universities and international partners, including Los Alamos National Laboratory in New Mexico; Sonoma State University, Rohnert Park, California; the University of Leicester, in Leicester, UK and University College London¿s Mullard Space Science Laboratory in Dorking, Surrey, UK; and the Brera Observatory of the University of Milan and ASI Science Data Center in Rome, Italy. The Swift spacecraft was built by General Dynamics C4 Division, Spectrum Astro, in Gilbert, Arizona.
Gamma Ray Bursts
Gamma-ray bursts have been puzzling scientists since they were discovered in 1969. They are the most powerful explosions in the universe, giving off in a few seconds the same energy as the Sun radiates in its entire 10 billion year life. Gamma-ray bursts probably occur when a very massive star dies in a powerful supernova explosion, creating a black hole at its centre.
X-ray flashes resemble a lower energy and longer-duration version of a gamma-ray burst, an energetic explosion thought to signal the death of a massive star. These flashes have many similarities to GRBs, and many theories have been put forward to explain the lack of gamma rays. They were discovered in only 5 years ago.