Soft X-ray response of a 36 pixel superconducting tunnel junction array for high-resolution X-ray astronomy.

The development of superconducting tunnel junction detector arrays has now reached a stage where practical applications in X-ray astrophysics can be considered. The arrays are based on tantalum devices, with operating temperatures of about 0.4 K. The energy resolution of these detectors is limited by Fano and tunnel noise to about 3 eV at 1 keV. The first results from a 6x6, tantalum based array are presented. These medium sized arrays have good energy resolution (2.5 and 6.8 eV at 270 and 1000 eV respectively) and adequate absorption efficiency (of order 80% and 30% at 500 and 1000 eV respectively). The possibility to operate and read out simultaneously more than one channel has been demonstrated. The uniformity of the array elements both in charge output and energy resolution is good, with the overall responsivity across the array varying by less than 5%. The energy resolution at X-ray energies is dominated by spatial non-uniformities in the individual pixel response. Such a performance allows us now to consider the development of a X-ray cryogenic camera based on STJ detectors. Provided the field coverage of these cameras can be extended through the development of larger format detector arrays, they have the potential to form a major basis for astrophysics instrumentation in the next century.