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arXiv · 2509.15851

Observation of Galactic center in the sub-MeV gamma-ray band with electron-tracking Compton camera

Tomonori Ikeda·Toru Tanimori·Atsushi Takada·Taito Takemura·Kei Yoshikawa·Yuta Nakamura·Ken Onozaka·Mitsuru Abe·Yoshitaka Mizumura
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Abstract

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 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 $(3.2~\pm~1.4) \times 10^{-2}$ photons cm$^{-2}$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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Tomonori Ikeda, Toru Tanimori, Atsushi Takada, Taito Takemura, Kei Yoshikawa, Yuta Nakamura, Ken Onozaka, Mitsuru Abe, Yoshitaka Mizumura. 2025-09-19. Observation of Galactic center in the sub-MeV gamma-ray band with electron-tracking Compton camera. https://doi.org/10.1103/h89s-4p7q

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