Design concept for a high altitude rotating modulator gamma-ray imager

A rotating modulator (RM) is capable of imaging hard x-rays and gamma rays by the temporal modulation of incident photons. It combines a single mask of equally-wide slats and slits, rotating above an array of detectors with diameter equal to the slats. Since the RM works in the temporal domain, appropriate analysis of the measured data enables super-resolution (resolution better than the geometric resolution), which consequently allows for larger detector elements, better efficiency at higher energies, and a simplified detector design. We describe the RM concept and discuss briefly a novel image reconstruction technique to achieve super-resolution and suppress fluctuations arising from noise. We present experimental results from a laboratory prototype and the concept and expected results for a high-altitude balloon flight of an RM. The High-Altitude Rotating Modulator for Energetic Radiation Imaging (HARMEnI) is a prototype balloon-borne instrument that offers a 20° field-of-view and 1.9° intrinsic resolution with a sensitivity in the range of 30-700 keV. At its intrinsic resolution, HARMEnI will obtain a 20σ observation of the Crab Nebula and Cygnus X-1 in approximately one hour. For a 1-day flight from Ft. Sumner, New Mexico, exposure times for these sources will exceed 3 hours, enabling enhancement of image resolution.