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J.D. Kurfess, W.N. Johnson, R.A. Kroeger (NRL), B.F. Phlips (GMU)
A high resolution Compton telescope has been identified by NASA's Gamma Ray Astronomy Program Working Group (GRAPWG) as the highest priority major mission in gamma ray astrophysics following GLAST. A target sensitivity of 2 x 10-7 g cm-2s-1 for narrow lines from discrete sources has been established. This would provide 25-100 times improved sensitivity, relative to CGRO and INTEGRAL. This sensitivity is essential to achieving several key science objectives, including solid detections of 10’s of Type Ia supernovae per year. Quantifying the production of radioactivities in these supernovae and following their light curves are key observations in developing a better understanding of the explosion mechanisms. A wide field-of-view ACT will also discover many Type Ia supernovae that may otherwise go undetected by optical observations due to obscuration or observational restrictions. An instrumental approach being investigated at NRL is the development and use of position-sensitive solid-state detectors (Ge, Si) for a high spectral resolution Compton telescope mission. We have shown that with only two Compton scatter interactions followed by a third interaction, the incident gamma ray energy and direction cone can be precisely determined in detectors with excellent energy and position resolution. Since full energy deposition is not required, a practical instrument can achieve high detection efficiencies. Furthermore, since only Compton interactions are required, thick silicon strip or pixel detectors are an attractive option for the detectors. Compton reconstruction of the detailed pattern of energy loss is also a powerful method to reject instrumental background. Together, these techniques enable the design of a Compton instrument that should meet the GRAPWG sensitivities.
Supported by the Office of Naval Research