Hard x-ray and gamma-ray imaging spectroscopy for the next solar maximum

Abstract

A single high-energy instrument based on rotating modulation collimators with germanium semiconductor spectrometers as the detectors can provide high angular resolution (< 1 arc sec), high time resolution (< 1 s), and high spectral resolution (about one keV), all in one package. Such rotating modulation- collimator optics provide excellent spatial (u,v)-plane coverage for high-contrast images in the hard X-ray domain, where there will be a large signal-to-noise ratio during even modest flares. The use of thick modulation plates will make it possible to image gamma rays with < 5 arc sec angular resolution to energies in excess of 10 MeV during the more energetic flares without compromising the ability of the germanium detectors to resolve the gamma-ray lines. Energetic neutrons will also be imaged for the first time with < 20 arc sec angular resolution. This combination of imaging and spectroscopy at high resolution will be a powerful tool for helping to answer central questions of solar flare physics, especially if such an instrument were supported by observations at longer wavelengths. The timing of solar activity dictates a launch of such a High-Energy Solar Physics (HESP) mission by 1998.