HEXAGONE observation of the Galactic Center gamma-ray continuum

The spectrum of the Galactic Center region obtained by the HEXAGONE germanium spectrometer in 1989 is analyzed with a new technique that accounts For the non-diagonal energy response of the instrument and atmosphere in a model-independent way. The continuum shows a distinct feature centered at 178 keV with a FWHM of 55 keV and flux 1.47 × 10 −3 photons/cm 2 /s. We discuss the contributions of point sources and diffuse Galactic emission to the continuum, and the possible interpretation of the 178 keV feature as Compton backscattering of radiation near 511 keV