Direct Measurement of the Cosmic-Ray Carbon and Oxygen Spectra from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>10</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>GeV</mml:mi><mml:mo>/</mml:mo><mml:mstyle mathvariant="italic"><mml:mi>n</mml:mi></mml:mstyle></mml:mrow></mml:math> to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>2.2</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>TeV</mml:mi><mml:mo>/</mml:mo><mml:mstyle mathvariant="italic"><mml:mi>n</mml:mi></mml:mstyle></mml:mrow></mml:math> with the Calorimetric Electron Telescope on the International Space Station
O. Adriani, Yosui Akaike, Katsuaki Asano, Y. Asaoka, M. G. Bagliesi, E. Berti, G. Bigongiari, W. R. Binns, M. Bongi, P. Brogi, A. Bruno, J. H. Buckley, N. Cannady, G. Castellini, C. Checchia, M. L. Cherry, G. Collazuol, Ken Ebisawa, H. Fuke, S. Gonzi, T. G. Guzik, T. Hams, K. Hibino, M. Ichimura, Kunihito Ioka, W. Ishizaki, M. H. Israel, K. Kasahara, J. Kataoka, Ryuho Kataoka, Y. Katayose, C. Kato, Norita Kawanaka, Y. Kawakubo, Kazuyoshi Kobayashi, Kazunori Kohri, H. Krawczynski, John Krizmanic, J. T. Link, P. Maestro, P. S. Marrocchesi, A. Messineo, J. W. Mitchell, Shoko Miyake, A. A. Moiseev, M. Mori, N. Mōri, Holger Motz, K. Munakata, S. Nakahira, Jun Nishimura, G. A. de Nolfo, S. Okuno, J. F. Ormes, N. Ospina, S. Ozawa, L. Pacini, F. Palma, P. Papini, B. F. Rauch, S. Ricciarini, Kazuhiro Sakai, T. Sakamoto, M. Sasaki, Yuki Shimizu, A. Shiomi, R. Sparvoli, П. Спиллантини, F. Stolzi, S. Sugita, J. E. Suh, A. Sulaj, M. Takita, T. Tamura, T. Terasawa, S. Torii, Y. Tsunesada, Y. Uchihori, E. Vannuccini, J. P. Wefel, K. Yamaoka, S. Yanagita, A. Yoshida, Kenji Yoshida
Abstract
In this paper, we present the measurement of the energy spectra of carbon and oxygen in cosmic rays based on observations with the Calorimetric Electron Telescope on the International Space Station from October 2015 to October 2019. Analysis, including the detailed assessment of systematic uncertainties, and results are reported. The energy spectra are measured in kinetic energy per nucleon from 10 GeV/n to 2.2 TeV/n with an all-calorimetric instrument with a total thickness corresponding to 1.3 nuclear interaction length. The observed carbon and oxygen fluxes show a spectral index change of ∼0.15 around 200 GeV/n established with a significance >3σ. They have the same energy dependence with a constant C/O flux ratio 0.911±0.006 above 25 GeV/n. The spectral hardening is consistent with that measured by AMS-02, but the absolute normalization of the flux is about 27% lower, though in agreement with observations from previous experiments including the PAMELA spectrometer and the calorimetric balloon-borne experiment CREAM.