S-CAM - an exciting new instrument sees first light on La Palma
3 February 1999
On 2 February, the Astrophysics Division's S-CAM instrument saw 'firstlight' at the 4.2m William Herschel Telescope on La Palma, observing thepulsar at the centre of the Crab nebula.S-CAM, a totally new instrument concept, is equipped with an array of'superconducting tunnel junctions' (STJ), small chips of the metaltantalum, cooled with the help of a bath of liquid helium to a temperaturewithin a degree of absolute zero.The Crab Pulsar provides an ideal target for verifying the camera's photoncounting and timingcapabilities. The figure shows the characteristic 'light curve' signatureof the pulsar: two beams of light which shine out, like a lighthouse, oneweak and long the other bright and short, in each revolution. These datawere obtained from just one of the 36 tantalum chips in S-CAM in a fourminute exposure.We started research into STJs in 1986, at first with the aim of developing a new detector for future X-ray astronomy missions. However it emerged that STJs were also sensitive at longer wavelengths, that is in the ultra-violet, optical and even infrared parts of the spectrum. Our attention therefore turned to developing an instrument that could be used in optical astronomy, with 'proof-of-concept' at a ground-based telescope.
The power of the STJ is that it can detect, with very high efficiency, single photons making up a beam of light and determine precisely both the arrival time and the wavelength, that is the colour, of individual photons - a unique combination. The STJ has applications, not only in astronomy but in the commercial and industrial fields, where fast measurements to capture transient phenomena in colour at very low light levels are required.
Discovered at radio wavelengths in 1968, the Crab pulsar is a neutron star spinning about 30 revolutions per second. The pulsar, together with a surrounding nebula, was left behind when a star, about 5000 light years away in the Taurus constellation, exploded as a supernova, appearing in 1054 AD.
The staff of the WHT at the Isaac Newton Group, in particular Peter Moore, are thanked for excellent support for this commissioning run.
