First Emulsion γ-Ray Telescope Imaging of the Vela Pulsar by the GRAINE 2018 Balloon-borne Experiment

Satoru Takahashi, Shigeki Aoki, Atsushi Iyono, Ayaka Karasuno, Kohichi Kodama, Ryosuke Komatani, Masahiro Komatsu, Masahiro Komiyama, Kenji Kuretsubo, Toshitsugu Marushima, Syota Matsuda, Kunihiro Morishima, Misaki Morishita, Naotaka Naganawa, Mitsuhiro Nakamura, Motoya Nakamura, Takafumi Nakamura, Yuya Nakamura, Noboru Nakano, Toshiyuki Nakano, Kazuma Nakazawa, Akira Nishio, Miyuki Oda, Hiroki Rokujo, Osamu Sato, Kou Sugimura, Atsumu Suzuki, Mayu Torii, Saya Yamamoto, and Masahiro Yoshimoto

We are developing the Gamma-Ray Astro-Imager with Nuclear Emulsion project, designed for 10 MeV–100 GeV cosmic γ-ray observations with a high angular resolution (5'/008 at 1–2 GeV) and a polarization-sensitive large-aperture (∼10 m2) emulsion telescope for repeated long-duration balloon flights. In 2018, a balloon-borne experiment was carried out in Australia with a 0.38 m2 sensitive area and a flight duration of 17.4 hr, including 6.7 hr of Vela observations. Significant improvements compared with the 2015 balloon-borne experiment were achieved by a factor of 5, including both an increase in effective area × time and a reduction in the background contribution. We aimed to demonstrate the telescope's overall performance based on detection and imaging of a known γ-ray source, the Vela pulsar. A robust detection of the Vela pulsar was achieved with a 68% containment radius of 042, at a significance of 6σ, at energies above 80 MeV. The resulting angular profile is consistent with that of a pointlike source. We achieved the current best imaging performance of the Vela pulsar using an emulsion γ-ray telescope with the highest angular resolution of any γ-ray telescope to date.

THE ASTROPHYSICAL JOURNAL

Springer

960:47

1

18

DOI 10.3847/1538-4357/ad0973