Measurement of gamma-rays above 1 GeV by ASTROMAG

The present study examines the feasibility of the application of a matter-antimatter spectrometer incorporating Astromag to measurement of gamma-rays. In the spectrometer under consideration, gamma-rays are converted to electron-positron pairs by an electromagnet and cryostat and the momentum vectors of these electrons and positrons are measures separately to determine the direction of the original gamma-rays. It is suggested that an about one-year observation with an Astromag R-D magnet performed on a space station will provide data of statistic significance on the isotropic and galastic components of diffuse gamma-rays up to several 10s GeV and 100 GeV, respectively. For gamma-rays from a point source, the magnet will have a sensitivity up to an integral flux of 7 x 10-9 photons-cm2 for gamma-rays above 1 GeV. It is expected, however, that GRO-EGRET has a higher potential for measurement up to about 30 GeV. The high resolution performance of Astromag is particularly advantageous in measuring monochromatic gamma rays in the GeV range. If they come from γγ pair annihilation, however, it seems difficult for an R-D magnet to provide data of statistic significance even when γ is the major component of the dark matter. (Nogami, K.)