Naoyuki Ota, Takuya Takahashi, Toru Tamagawa, Tomoshi Takeda, Teruaki Enoto, Takao Kitaguchi, Wataru Iwakiri, Yo Kato, Masaki Numazawa, Tatehiro Mihara, Hiromitsu Takahashi, Chin-Ping Hu, Yuanhui Zhou, Keisuke Uchiyama, Yuto Yoshida, Syoki Hayashi, Arata Jujo, Sota Watanabe, Amira Aoyama, Satoko Iwata, Kaede Yamasaki, Soma Tsuchiya, Yosuke Nakano, Takayuki Kita, Mayu Ichibakase, Hiroki Sato, Hirokazu Odaka, Tsubasa Tamba, Kentaro Taniguchi

This study demonstrated the pulsar navigation capability of the CubeSat X-ray observatory NinjaSat, which is equipped with two Gas Multiplier Counters (GMCs). The GMCs are sensitive to the 2-50 keV energy band and have an effective area of 16 cm^2 per module at 6 keV. We verified the timing accuracy by observing the Crab Pulsar and confirmed stable timing performance within 100 microseconds. To demonstrate pulsar navigation, we applied a method that optimizes orbital parameters to maximize the significance of the pulsar X-ray pulse profile, known as the Significance Enhancement of Pulse-profile with Orbit-dynamics (SEPO) method. We observed the Crab Pulsar with a total exposure of approximately 100 ks at different epochs and analyzed the data transmitted to the ground. By comparing the optimized orbit with the satellite position derived from Global Positioning System data, we quantitatively evaluated the navigation performance. The results show that the position component along the Crab line of sight was consistently constrained within approximately 40 km, and the three-dimensional position error ranged from 27 to 370 km depending on the observation epoch. These results demonstrate the feasibility of applying a CubeSat-class X-ray observatory to pulsar navigation and provide the first experimental verification that the accuracy of the SEPO method depends on the seasonal geometry between the orbital plane and the pulsar direction.