水村 好貴

[This paper was featured in Nature Research Highlights (Nature, 656, 542 (2026)).] 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⁢𝜎 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 point-like source, a multi-component 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 multi-component model is (3.2±1.4)×10−2photonscm−2s−1, consistent with the value reported by INTEGRAL within 1⁢𝜎. These results establish the potential of the ETCC for future high-precision MeV gamma-ray surveys.