A perspective view to hard-X-ray astronomy

Summary The present observational and instrumental status of hard-X-ray astronomy ((10÷200) keV) is discussed. The relevance of observations in this energy range is stressed and a few examples of unsolved observational problems in galactic and in extragalactic astronomy are discussed. In these examples we focus on the possibility to solve the problems with observations using detectors of the current generation. In this framework, the performances of the most sensitive hard-X-ray detectors are discussed with particular emphasis on the control of systematic errors. Quite simple but unavoidable considerations on limits of the present generation of hard-X-ray detectors (supported by results of simple simulations) lead to the conclusion that a decisive breakthrough can be achieved only using optics with a sufficiently good concentration power. In particular we discuss the feasibility of hard-X-ray telescopes (with a concentration power ≫1), using either grazing incidence or Bragg diffraction. The use of concentrators in this energy band can also make feasible polarimetric measures of a substantial sample of X-ray sources, up to now severely limited by the very low detection efficiency of the devices used in polarimetry. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.