ABSTRACT
Telescope technology in the hard X-ray band of 10-100 keV is undergoing rapid transformation. This band is prime for the study of high-energy, nonthermal astrophysical processes, since thermal emission from stars and diffuse plasma dominates most of the sky from the infrared up to soft X-rays at around 10 keV. Examples of nonthermal phenomena of interest in hard X-ray astronomy include the so-called diffuse X-ray background, peaking in energy ux at 30 keV, inverse Compton scattering of lower-energy photons by relativistic electrons in the haloes of clusters of galaxies and the radio lobes of active galaxies, and synchrotron and both line emission and absorption in stellar remnants such as young supernova remnants and pulsars. Our understanding of these phenomena is limited by the imaging, spectral, and timing capabilities of hard X-ray detectors currently in orbit. Further advances thus require the development of new detection technologies specically for hard X-ray astronomy, for which most sources are extremely faint, and observation time is always limited. In the past decade, several telescope projects have contributed to this goal using the scientic balloon platform. In this chapter, we recount the detector development effort in one representative project, the High Energy Focusing Telescope (HEFT).1
