Instrumentation for gamma-ray astronomy

Abstract

There are three distinct energy ranges within the broad spectrum of gamma-ray astronomy, low energy (which in turn is subdivided), high energy, and very high and ultra-high energy. Each has its own unique type of instrumentation. Only in the very high-energy range do the telescopes bear any resemblence to optical telescopes; the rest appear more like instrumentation for high-energy physics. The low-and high-energy ranges are now primarly dependent on spaceflight, although some balloon altitude research is still being accomplished. Satellites planned to be launched in the next two years will carry telescopes with considerably more capability than those previously flown in space. In the very high and ultra-high energy realm, large ground based systems are used to detect the secondary radiation from interactions of the gamma radiation with the air. In all cases, software and data analysis are becoming increasingly important aspects of the subject as the data become ever greater and more complex. Beyond the telescopes to be flown in space or installed on the ground soon, instrumentation, taking advantage of new detector techniques which have come into being or older ones which now seem capable of being adapted to space, are being developed for the more distant future.

Science applications of the Mars Observer gamma ray spectrometer

“…In this design, the radiative heat leak to the cold stage is greatly reduced by an arrangement of lightweight, 1ow-emittance, highly specular and reflective radiation shields [Bard et al, 1982;Bard, 1984]. Large V-shaped cavities are created by arranging adjacent shields that expand outward from the cold stage [Bertsch et al, 1988]. The shields intercept the radiation from the warm surroundings and by multiple reflections direct the energy to space.…”

About cosmic gamma ray lines

“…In this MeV energy range, instrumental backgrounds are relatively large, because in absence of concentrators for incoming gamma rays the detector surface defining the collection area must be large. But activation by cosmic rays of the instrument materials generates a large instrumental background, which is proportional to the instrument mass and thus also scales up with increasing detector sizes [10]. Therefore, in principle, it is best to maximise the active detector mass and minimise any non-active instrument masses.…”

“…The treatments of instrumental background and the extraction of weak cosmic line signals therein have been the major challenges in that field [10,19,20,21], and are decisive for instrument performances beyond the constraints given from gamma ray detector physics. The sensitivity currently reached for a typical observing time of 10 6 s is about 10 −5 ph cm −1 s −1 , so that we were only able to measure the brightest of the expected variety of gamma-ray line sources.…”

New insights from cosmic gamma rays

“…The first Galaxy-scale sources seen in such gamma rays were the lines attributed to positron annihilation reported after a balloon experiment from the central Galaxy in 1964 and the line from 26 Al radioactivity gamma-rays also from the central Galaxy region reported from the 1978/79 measurements with the HEAO-C satellite [56]. But it took many years to further advance the techniques of gamma-ray telescopes, mainly due to the penetrating nature of the gamma rays, which prevent photon collection and concentration by mirrors or lenses, and due to activation by cosmic rays of the instrument materials to generate a large instrumental background [1]. Therefore, even after two major observatory missions for imaging and spectroscopy [33,78,98,89,19], currently achieved sensitivities allow to only see Galactic sources and exceptionally-bright supernovae from up to few Mpc distance, and spatial resolution is of order 2-3 degrees only.…”