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The final instrument on board Swift, the satellite launched in November last year to hunt for gamma-ray bursts, has been switched on, and the space lab is now fully operational. The ultra-violet optical telescope (UVOT) has sent its first picture back to Earth, and is poised to snap its first gamma-ray burst.

The false colour image is of the Pinwheel galaxy, M101, regarded by many as the perfect spiral galaxy. The picture shows hot, star forming regions on the arms of the galaxy, while the centre is older, and cooler.

The picture was created by combining light from several of the UVOT's filters, all the way from invisible-to-humans ultraviolet, to the blues and yellows of the visible spectrum. In the image, however, the shortest wavelengths are represented as blue, while the longest are coloured in red.

Swift will investigate gamma-ray-bursts, the most violent, and mysterious explosions in the universe. It has been designed to respond rapidly to detection of gamma rays - within 20-70 seconds. This is vital as the whole explosion can be over in as little as 200 seconds.

Professor Keith Mason, the UK UVOT lead at University College London commented: "The UVOT isn't as powerful as [observatories like Hubble, or Keck], but has the advantage of observing from the very dark skies of space. Moreover, it will start observing the burst afterglow within minutes, as opposed to the day or week long delay inherent with heavily used observatories. This is extremely important because the bulk of the afterglow fades within hours."

The UVOT is the third of Swift's observing instruments that will come into play, after the Burst Alert Telescope and the X-Ray Telescope. It can pinpoint a gamma ray source to sub-arcsecond accuracy, the equivalent of the eye of a needle held at arms length, PPARC (Particle Physics and Astronomy Research Council) helpfully informs us.

It will reveal more about the behaviour of this ultraviolet afterglow, such as the temperature and velocity of material ejected during the explosion. Knowing how the afterglow is shaped, and how it fades will give researchers an insight into the explosion that preceded it.

Peter Roming, UVOT lead scientist at Penn State, notes that we know next to nothing about this stage of a burst. "This is because the atmosphere blocks most ultraviolet rays from reaching telescopes on Earth, and there have been few ultraviolet telescopes in orbit. We simply haven't yet reached a burst fast enough with a UV telescope." ®

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What you need to know about cloud backup