First results on the search for the Galactic Center Excess in the sub-GeV band with the emulsion telescope in GRAINE 2023
Year: 2026
Type: preprint
Abstract: (Please check the paper for full abstract.) The Galactic Center Excess (GCE) is an unexplained excess of gamma-ray emission from the Galactic Center. The GRAINE experiment aims to reveal the origin of the GCE using an emulsion gamma-ray telescope with high angular resolutions of 1 deg at 100 MeV and 0.1 deg at 1 GeV. In this study, we search for the GCE in a small region near the Galactic Center using the GRAINE 2023 flight data. In particular, rather than focusing on the spectral peak of the GCE at 2 GeV, we focused on the energy range below 300 MeV, where the spectral differences between the dark matter annihilation and millisecond pulsar scenarios are more pronounced. We searched for the GCE within 1 deg of the Galactic Center in the 75--300 MeV energy range. Although no significant excess was observed, we obtained an upper limit on the GCE flux of 1.70*10^-7 GeV cm^-2 s^-1 at the 2 sigma confidence level for the 1deg-radius ROI centered on the Galactic Center, based on a direct observation of the narrow region around the Galactic Center. This observation requires high angular resolution and represents a unique result from GRAINE. The obtained upper limit is consistent with the GCE flux near the Galactic Center, which was estimated from existing Fermi-LAT observations using a wide ROI and assuming an NFW profile. Although the current upper limit constrains some models, the available statistics are still insufficient to distinguish between the dark matter annihilation and millisecond pulsar scenarios, and both remain consistent with the current results. We also estimated the projected sensitivity of future GRAINE experiments based on the present observation and demonstrated their potential to probe the origin of the GCE by comparing the projected sensitivity with the predicted GCE spectra.
Source: arXiv (Cornell University)
Authors: Nakamura, Yuya, Aoki, Shigeki, Azuma, Takashi, Hayashi, Hirotaka, Isayama, Yudai, Iyono, Atsushi, Kato, Takumi, Kawahara, Tsuyoshi, Kodama, Kohichi, Komatani, Ryosuke, Komatsu, Masahiro, Komiyama, Masahiro, Minami, Hideyuki, Morishima, Kunihiro, Murakami, Fumiya, Nagahara, Shogo, Naganawa, Naotaka, Nakamura, Mitsuhiro, Nakamura, Tomoaki, Nakano, Noboru, Nakano, Toshiyuki, Nakazawa, Kazuma, Oda, Miyuki, Okamoto, Kazuhiro, Rokujo, Hiroki, Sato, Osamu, Shimizu, Kai, Suganami, Amon, Sugi, Yuki, Sugimura, Kou, Takahashi, Satoru, Usuda, Ikuya, Yamamoto, Saya, Yamashita, Jun, Yamashita, Mayu, Yoneno, Shoma, Yoshimoto, Masahiro
Institutions: Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Kobe University, Okayama University of Science, Aichi University of Education, University of Fukui, Gifu University, Research Institute of Nuclear Engineering, University of Fukui, RIKEN Nishina Center
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Awards: Nuclear Emulsion - New deployments for fundamental and interdisciplinary researches in the 21st century-, パルサーとGRBの詳細観測を可能にする原子核乾板時刻付与機構の開発, Cosmic gamma-ray observation by balloon borne emulsion telescope to study unsolved issues, パルサー磁場構造解明のためのガンマ線偏光観測の開拓, GeV/sub-GeV宇宙ガンマ線の世界初偏光観測によるパルサー磁場構造解明, Unveiling the mystery of GeV/sub-GeV cosmic gamma rays by a balloon-borne emulsion te lescope, Polarization measurement for high energy gamma-ray sources with the nuclear emulsion, 原子核乾板望遠鏡による高エネルギーガンマ線偏光観測の実現, Realization of a time-resolved nuclear emulsion detector using a multi-stage shifter and its application to cosmic gamma-ray observation, Probing Dark Matter with the Highest Angular Resolution Cosmic Gamma Ray Observations ~Development of the World's Largest Aperture Emulsion Telescope, Development of large-aperture emulsion gamma-ray telescopes for high-angular resolution observation of the galactic center
OpenAlex ID: W7213222624