First results on the search for the Galactic Center Excess in the sub-GeV band with the emulsion telescope in GRAINE 2023

@misc{nakamura2026first,
  title = {{First results on the search for the Galactic Center Excess in the sub-GeV band with the emulsion telescope in GRAINE 2023}},
  author = {Yuya Nakamura and Shigeki Aoki and Takashi Azuma and Hirotaka Hayashi and Yudai Isayama and Atsushi Iyono and Takumi Kato and Tsuyoshi Kawahara and Kohichi Kodama and Ryosuke Komatani and Masahiro Komatsu and Masahiro Komiyama and Hideyuki Minami and Kunihiro Morishima and Fumiya Murakami and Shogo Nagahara and Naotaka Naganawa and Mitsuhiro Nakamura and Tomoaki Nakamura and Noboru Nakano and Toshiyuki Nakano and Kazuma Nakazawa and Miyuki Oda and Kazuhiro Okamoto and Hiroki Rokujo and Osamu Sato and Kai Shimizu and Amon Suganami and Yuki Sugi and Kou Sugimura and Satoru Takahashi and Ikuya Usuda and Saya Yamamoto and Jun Yamashita and Mayu Yamashita and Shoma Yoneno and Masahiro Yoshimoto},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.14551},
  eprint = {2609.14551},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.14551},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - First results on the search for the Galactic Center Excess in the sub-GeV band with the emulsion telescope in GRAINE 2023
AU  - Yuya Nakamura
AU  - Shigeki Aoki
AU  - Takashi Azuma
AU  - Hirotaka Hayashi
AU  - Yudai Isayama
AU  - Atsushi Iyono
AU  - Takumi Kato
AU  - Tsuyoshi Kawahara
AU  - Kohichi Kodama
AU  - Ryosuke Komatani
AU  - Masahiro Komatsu
AU  - Masahiro Komiyama
AU  - Hideyuki Minami
AU  - Kunihiro Morishima
AU  - Fumiya Murakami
AU  - Shogo Nagahara
AU  - Naotaka Naganawa
AU  - Mitsuhiro Nakamura
AU  - Tomoaki Nakamura
AU  - Noboru Nakano
AU  - Toshiyuki Nakano
AU  - Kazuma Nakazawa
AU  - Miyuki Oda
AU  - Kazuhiro Okamoto
AU  - Hiroki Rokujo
AU  - Osamu Sato
AU  - Kai Shimizu
AU  - Amon Suganami
AU  - Yuki Sugi
AU  - Kou Sugimura
AU  - Satoru Takahashi
AU  - Ikuya Usuda
AU  - Saya Yamamoto
AU  - Jun Yamashita
AU  - Mayu Yamashita
AU  - Shoma Yoneno
AU  - Masahiro Yoshimoto
PY  - 2026
DA  - 2026/09/25
PB  - arXiv
DO  - 10.48550/arxiv.2609.14551
UR  - https://arxiv.org/abs/2609.14551
AB  - (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.
ER  -