We report the direct detection of gamma-ray emission from the Galactic Center in the 150–600 keV band using the electron-tracking Compton camera (ETCC), which has a wide field of view of 3.1 sr. This represents the first application of this linear, imaging-spectroscopy method to observations of the Galactic Center. Measurements in a one-day flight over Australia yielded significant gamma-ray detection in the light curve and revealed a $7.9\sigma$ excess over the background in the image map from the Galactic Center region. These results, obtained through a simple and unambiguous analysis, demonstrate the high reliability and sensitivity of the ETCC and establish its potential for future high-precision MeV gamma-ray observations. The measured intensity and spatial distribution were tested against three emission models: a single pointlike source, a multicomponent structure, and a symmetric two-dimensional Gaussian. All three were found to be statistically consistent with the data. The positronium-related flux provided by the multicomponent model is $(3.2\pm 1.4)\times {10}^{-2}$ photons ${\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$, consistent with the value reported by INTEGRAL within $1\sigma$. These results establish the potential of the ETCC for future high-precision MeV gamma-ray surveys.

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• Gamma ray astronomy