8.3 SUPPORTING PROGRAMS

8.3.1 TECHNOLOGY DEVELOPMENT and BALLOON PROGRAM

The future vitality of hard X-ray and gamma-ray astronomy depends critically on the development of new instrumentation with significantly enhanced capabilities over current hardware. The key steps in this process are: 1) basic detector, aperture and electronics technology development; 2) instrument building; 3) laboratory and accelerator testing; and 4) balloon-flight performance verification. All of these activities are currently funded under the NASA high energy astrophysics Supporting Research and Technology (SR&T) program. The growing over subscription to the SR&T program indicates that the available funding is falling below the community's needs. The GRAPWG recommends that the SR&T funding level be increased and/or other funding be found, such as through the Advanced Technology (ATD) program. The GRAPWG views NASA's balloon program as highly successful and essential for the continuing vitality of our field. The importance of the program is increasing as faster space flight opportunities like SMEX and MIDEX require fully proven technology. The program also continues to be an avenue for scientific research. Enhance-ments to the program, like long-duration capability, are encouraged.

8.3.2 DATA ANALYSIS and THEORY

The current revolution in our understanding of the high-energy sky is the result of detailed data analysis and theoretical study of the data from the new missions. Much of the recent progress in understanding energetic continuum sources has resulted from a careful comparison of data from many missions, with support from ground-based studies. The GRAPWG recommends support for such correlative studies in the MO&DA and Astrophysics Data Programs. Because multiwavelength investigations often require years to assemble the key data, the Long-Term Space Astrophysics Research Program has particular relevance to high-energy investigations. Further, in view of the many outstanding puzzles in the gamma-ray regime, vigorous fundamental study of exotic high-energy sources remains essential. The Astrophysics Theory Program provides the primary support for these investigations.

8.3.3 TeV ASTRONOMY

An important extension to high energy gamma-ray studies is provided by ground-based observations in the TeV range. The current energy threshold of ~0.1 TeV could be lowered into the 10's of GeV range for critical overlap with a future high energy space mission if new proposed telescopes are funded. An example of the science possible with such broad band coverage is the study of the intergalactic infrared radiation density via measurements of cut offs in AGN spectra due to photon-photon (gamma-IR) pair production. The GRAPWG strongly endorses the development of new telescopes for TeV astronomy. Investment in the operation and improvement of ground-based (atmospheric Cherenkov) gamma-ray observatories by the appropriate funding agencies (U.S. Department of Energy, National Science Foundation, Smithsonian Institution) should proceed with the aim of having a third-generation telescope in operation by the launch date of the High-Energy Intermediate Mission (see section 8.1.1).

 8.4 NEW TECHNOLOGIES

New detector and imaging technologies promise to revolutionize the field of hard X-ray and gamma-ray astronomy. They offer significant improvements in performance over existing hardware while being lower in cost. Some of these are mature developments that are near flight readiness while others are showing promise in the lab but still need significant development. A vigorous program of research and development is essential to bring these technologies to fruition. The technologies needed to support the recommended new missions include the following:

• Detectors for tracking electrons and positrons in pair telescopes. Examples are strip detectors, gas microstrips, and scintillation fibers. These offer better position resolution than spark chambers and have much longer lifetimes.

• Mirrors with multilayer coatings that extend focusing optics into the 10-100 keV range. Alternating layers of low- and high-atomic number coatings on X-ray mirrors can focus photons up to ~100 keV. With image concentration onto a position sensitive detector, the detector and sky background for a point source of interest can be negligible, allowing much deeper observations than the current background-limited instruments.

• Liquid and high-pressure-gas detectors for keV through MeV astronomy. The high density and atomic number of Xe offers good stopping power. Large volume liquid time projection chambers with finely segmented electrodes for high spatial resolution are feasible. They combine high detection efficiency with good energy resolution and three-dimensional imaging.

• Cadmium zinc telluride detectors for hard X-ray astronomy. The high density and atomic number of CdZnTe give good stopping power, and the large band gap allows room temperature operation. Large-area arrays can be easily and inexpensively implemented. Fine segmentation of the electrodes can give high spatial resolution.

• Germanium detectors with finely segmented electrodes. These detectors must be cryogenically cooled, but offer the best energy resolution of existing mature technologies and now can also have high spatial resolution.

• Very Large Scale Integration (VLSI) of custom low-power analog circuits. These devices enable detector systems utilizing millions of signal channels. Such systems are components of several of the recommended new missions.