GRAINE2023: Sub-GeV/GeV gamma-ray observation with a high angular resolution by the balloon borne emulsion telescope

Y. Nakamura*, Y. Isayama, I. Usuda, T. Kawahara, M. Komiyama, K. Sugimura, T. Nakano, S. Nagahara, T. Nakamura, M. Nakamura, H. Hayashi, H. Minami, S. Yamamoto, H. Rokujo, S. Akita, A. Iyono, Y. Sugi, F. Murakami, K. Nakazawa, M. Yoshimoto, S. Aoki, T. Azuma, K. Okamoto, M. Oda, T. Kato, S. Takahashi, J. Yamashita, M. Yamashita, S. Yoneno and G. Collaboration"

We have been running the GRAINE project, a cosmic gamma-ray observation project covering the energy range from 10 MeV to 100 GeV, using nuclear emulsion detectors characterized with a high-angular resolution, polarization sensitivity and large aperture area. We conducted the fourth balloon experiment, GRAINE2023, in Australia with an aperture area of 2.5 m2, for which we developed a new large-area telescope for scientific observations. We detected the Vela pulsar, thereby verifying the performance of the newly developed telescope. The measured angular resolution is 0.59+0.1−0.07 ∘ for energies above 75 MeV, primarily in the 100--500 MeV range. We then measured the gamma-ray spatial distribution near the Galactic Center for energies above 75 MeV, and the obtained results are consistent with the expected models derived from Fermi-LAT observations. Because the angular resolution of Fermi-LAT is about 1∘ at 1 GeV, obtaining the flux within 1∘ of the Galactic Center in the sub-GeV energy range requires assumptions based on observational results at energies above 1 GeV. By contrast, we achieved a direct measurement of the flux within 1∘ of the Galactic Center, enabled by the high angular resolution of GRAINE. This represents a unique feature of the present study.

Proceedings of Science

SISSA, the International School for Advanced Studies based in Trieste

501

778

https://doi.org/10.22323/1.501.0778

https://pos.sissa.it/501/778/