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NASA re-schedules Swift launch

Probing the secrets of Gamma Ray Bursters

By Lucy Sherriff, 25 Oct 2004

The launch date for NASA's Swift satellite - designed to detect and analyse gamma ray bursters - has been delayed thanks to a faulty third stage rocket on an unrelated launch. The mission has been given a new provisional launch date of 11 November. Scientists involved in the project expect this to be confirmed within days.

Swift has been designed to detect and locate gamma ray bursts (GRB) more quickly and with greater accuracy than ever before. At the moment, astronomers detect between one and two GRB's every month, but when Swift is fully operational, this number will rise to around two per week.

The researchers will investigate four main questions: how is a GRB formed; what is the basic physics involved; is there just one kind, or many sub-classes; and what can they tell us about the early universe? Currently, astronomers believe GRBs are formed in one of two ways: from a super-giant star collapsing in on itself to form a black hole, or from the collision of two neutron stars in a decaying binary orbit, again, forming a black hole.

Whatever the precise mechanism, the result is a two jets of material expelled along the spin axis of the new body at a significant fraction of the speed of light. They are also extremely short lived, lasting anything from less than a second to a few minutes. Once it detects a burst, Swift will turn its telescopes towards the explosion within 20-70 seconds - much faster than current response times of hours, or even days.

Professor Keith Mason at University College, London's (UCL) Mullard laboratory, describes the bursts as being designed for superlatives as they are the largest explosions we have detected in the universe, ever. To get anything bigger, you need to invoke the big bang.

The jets are incredibly energetic and extremely bright, and involve a lot of gamma radiation. If one was to form at the centre of our galaxy, it would appear to us to be as bright as the sun. He explains that if one were to form that close it might also boil off the atmosphere, so its probably best not to dwell on that idea for too long.

In fact GRBs are so bright, that they could be detected as far back as the earliest five percent of the universe's life time. Since making a GRB needs a star to collapse, their presence is conclusive proof of star formation. The further back we find them, the more we learn about the early universe.

The satellite has three main instruments on board to try to answer the questions: the Burst Alert Telescope (BAT), the X-Ray telescope, and the Optical and UV telescope. The UK has taken a lead role in building the latter two. Once the BAT spots the burst it can determine its position to within four arcminutes, and sends this information to observers on the ground.

The satellite's automated response system will then kick in and swivel the craft round so that its other instruments are trained on that spot of sky. The X-Ray telescope can narrow the field still further to around 5 arcseconds, and the optical instrument to sub-arcsecond accuracy. All this will happen within 300 seconds.

Back on the ground, a network of robotic telescopes will swing into action, and researchers will also be able to call on some of the largest optical and radio telescopes to make further observations. Hubble and other orbital observatories may join in too.

Once the satellite is in orbit, it will begin a month-long period of testing and calibration. The instruments will be partially switched on during this phase, while the team confirms that the satellite can track areas of the sky without pointing at the sun, the moon or the earth, any of which would fry its delicate instruments.

All being well, Swift should be fully operational from the end of March 2005. ®

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