Measurement of the Iron Spectrum in Cosmic Rays 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:mi>n</mml:mi></mml:mrow></mml:math> to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>2.0</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>TeV</mml:mi><mml:mo>/</mml:mo><mml:mi>n</mml:mi></mml:mrow></mml:math> with the Calorimetric Electron Telescope on the International Space Station
O. Adriani, Yosui Akaike, Katsuaki Asano, Y. Asaoka, 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, P. Papini, B. F. Rauch, S. Ricciarini, Kazuhiro Sakai, T. Sakamoto, M. Sasaki, Yuki Shimizu, A. Shiomi, П. Спиллантини, F. Stolzi, S. Sugita, 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
The Calorimetric Electron Telescope (CALET), in operation on the International Space Station since 2015, collected a large sample of cosmic-ray iron over a wide energy interval. In this Letter a measurement of the iron spectrum is presented in the range of kinetic energy per nucleon from 10 GeV/n to 2.0 TeV/n allowing the inclusion of iron in the list of elements studied with unprecedented precision by space-borne instruments. The measurement is based on observations carried out from January 2016 to May 2020. The CALET instrument can identify individual nuclear species via a measurement of their electric charge with a dynamic range extending far beyond iron (up to atomic number Z=40). The energy is measured by a homogeneous calorimeter with a total equivalent thickness of 1.2 proton interaction lengths preceded by a thin (3 radiation lengths) imaging section providing tracking and energy sampling. The analysis of the data and the detailed assessment of systematic uncertainties are described and results are compared with the findings of previous experiments. The observed differential spectrum is consistent within the errors with previous experiments. In the region from 50 GeV/n to 2 TeV/n our present data are compatible with a single power law with spectral index -2.60±0.03.