Mission to find origins of biggest blast in space is set for launch

Known as gamma-ray bursts (GRB) they shine hundred of times brighter that a typical supernova and a million trillions times as bright as the Sun. While the bursts are common they occur randomly and are often fleeting, making it difficult for researchers to analyse both the burst and its afterglow.

Now with the launch next month of Swift, the first spacecraft specifically designed to study the afterglow of gamma-ray bursts, the NASA headed mission aims to determine the origin of gamma-ray bursts and classify them in a bid to learn more about the early universe.

Leading the UK's efforts in the mission are UCL's Mullard Space Science Laboratory (MSSL) and the University of Leicester, who provided core elements of the narrow field instruments, the X-ray telescope and the UV/optical telescope.

Professor Keith Mason, of UCL's Mullard Space Science Laboratory and UK Lead Investigator for UV/optical Telescope Team, explains:

"Swift is the first spacecraft specifically designed to study the afterglow of gamma-ray bursts across the electromagnetic spectrum, thereby getting the 'big picture'. Until now it has proved very difficult to observe several different wavelengths at once. For an orbiting observatory the Earth gets in the way at different times for each spacecraft, while on ground-based telescopes you have the added complication of cloud and bad weather. In addition Swift will allow us to analyse a large number of burst in the same way so their properties can be catalogued and compared."

The UV/optical telescope was built at MSSL using designs based on a MSSL telescope currently in operation on ESA's XMM-Newton Observatory. Designed to measures the optical and UV emission from a burst, the UV/optical telescope, will work along side the X-ray telescope, which measures X-ray emissions and the wide field Burst Alert Telesope (BAT), which reads the hard X-rays/Gamma rays.

Within seconds of detecting a burst in the BAT, the spacecraft will 'swiftly' re-point itself to aim the X-ray telescope and the UV/optical telescope on the burst to enable high precision measurements to be made of how the emission from the burst 'cools' with time, accompanied by a shift in the peak of the emission to lower and lower wavelengths.

"The optical design of the UV/optical telescope is basically very similar to any other reflecting telescope such as Celestron's that you can buy for amateur observing," says Professor Mason.

"The exception is that the UV/optical telescope is engineered much more rigorously to withstand the harsh operating environment of space, and to reap maximum advantage from not having to observe through a hazy unstable atmosphere. It uses high-speed detectors developed at UCL, which can record the position and time of individual photons of light, making it extremely sensitive.

"The instrument also contains clever onboard software which allows it to observe autonomously, to protect itself in the event of accidental exposure to very bright sources, and to manipulate the data collected to maximise the information transmitted to the ground.

"The UV/optical telescope is sensitive to photons in the blue range of the optical spectrum, and in the near ultraviolet, which cannot be observed from the ground because it is absorbed by the Earth's atmosphere. By monitoring how the emission from the burst fades, it will give clues as to the geometry and size of the emitting jet, and search for evidence of a re-brightening of the burst that might be caused by a supernova explosion in the star from which the burst originated.

"By comparing the way the emission of the burst changes with wavelength, or colour, we will be able to make a direct estimate of the distance of the burst. The UV/optical telescope will also provide a precise location for the burst."

Swift is set to launch on 11 November 2004 at Cape Canaveral, Florida.

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