High Spectral Resolution X-ray Observations of the Evolved Supermassive Stellar Binary System $\eta$ Carinae - Iron K$\alpha$ Band Profile Revealed with XRISM


Journal article


Xrism collaboration, M. Audard, H. Awaki, R. Ballhausen, A. Bamba, E. Behar, R. Boissay-Malaquin, L. Brenneman, Gregory V. Brown, M. Corcoran, Lia Corrales, E. Costantini, R. Cumbee, M. Trigo, C. Done, T. Dotani, K. Ebisawa, M. Eckart, D. Eckert, Satoshi Eguchi, T. Enoto, Y. Ezoe, A. Foster, R. Fujimoto, Y. Fujita, Yasushi Fukazawa, Kotaro Fukushima, A. Furuzawa, L. Gallo, Javier A. García, E. Goto, Liyi Gu, M. Guainazzi, Kouichi Hagino, Kenji Hamaguchi, I. Hatsukade, K. Hayashi, T. Hayashi, N. Hell, E. Hodges-Kluck, A. Hornschemeier, Y. Ichinohe, Shun Inoue, D. Ishi, Manabu Ishida, Yukiko Ishihara, K. Ishikawa, Y. Ishisaki, F. Junqueira, J. Kaastra, T. Kallman, Y. Kanemaru, Erin Kara, S. Katsuda, R. Kelley, C. Kilbourne, S. Kitamoto, S. Kobayashi, T. Kohmura, A. Kubota, M. Leutenegger, Michael Loewenstein, Yoshitomo Maeda, M. Markevitch, Hironori Matsumoto, K. Matsushita, D. McCammon, Brian McNamara, F. Mernier, B. V. Meulen, E. Miller, Jon M. Miller, I. Mitsuishi, Asca Miyamoto, M. Mizumoto, T. Mizuno, K. Mori, K. Mukai, Hiroshi Murakami, R. Mushotzky, H. Nakajima, K. Nakazawa, J. Ness, K. Nobukawa, M. Nobukawa, H. Noda, H. Odaka, S. Ogawa, A. Ogorzałek, T. Okajima, Naomi Ota, S. Paltani, R. Petre, P. Plucinsky, F. Porter, K. Pottschmidt, Kosuke Sato, Toshiki Sato, Makoto Sawada, H. Seta, M. Shidatsu, A. Simionescu, Randall Smith, Hiromasa Suzuki, A. Szymkowiak, Hiromitsu Takahashi, M. Takeo, T. Tamagawa, Keisuke Tamura, Takaaki Tanaka, A. Tanimoto, M. Tashiro, Y. Terada, Y. Terashima, Y. Tsuboi, M. Tsujimoto, H. Tsunemi, T. Tsuru, Aysegul Tumer, Hiroyuki Uchida, N. Uchida, Y. Uchida, H. Uchiyama, S. Ueda, Y. Ueda, S. Uno, J. Vink, S. Watanabe, Brian J. Williams, Satoshi Yamada, S. Yamada, Hiroya Yamaguchi, K. Yamaoka, N. Yamasaki, M. Yamauchi, S. Yamauchi, T. Yaqoob, T. Yoneyama, Tessei Yoshida, M. Yukita, I. Zhuravleva
2026

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APA   Click to copy
collaboration, X., Audard, M., Awaki, H., Ballhausen, R., Bamba, A., Behar, E., … Zhuravleva, I. (2026). High Spectral Resolution X-ray Observations of the Evolved Supermassive Stellar Binary System $\eta$ Carinae - Iron K$\alpha$ Band Profile Revealed with XRISM.


Chicago/Turabian   Click to copy
collaboration, Xrism, M. Audard, H. Awaki, R. Ballhausen, A. Bamba, E. Behar, R. Boissay-Malaquin, et al. “High Spectral Resolution X-Ray Observations of the Evolved Supermassive Stellar Binary System $\Eta$ Carinae - Iron K$\Alpha$ Band Profile Revealed with XRISM” (2026).


MLA   Click to copy
collaboration, Xrism, et al. High Spectral Resolution X-Ray Observations of the Evolved Supermassive Stellar Binary System $\Eta$ Carinae - Iron K$\Alpha$ Band Profile Revealed with XRISM. 2026.


BibTeX   Click to copy

@article{xrism2026a,
  title = {High Spectral Resolution X-ray Observations of the Evolved Supermassive Stellar Binary System $\eta$ Carinae - Iron K$\alpha$ Band Profile Revealed with XRISM},
  year = {2026},
  author = {collaboration, Xrism and Audard, M. and Awaki, H. and Ballhausen, R. and Bamba, A. and Behar, E. and Boissay-Malaquin, R. and Brenneman, L. and Brown, Gregory V. and Corcoran, M. and Corrales, Lia and Costantini, E. and Cumbee, R. and Trigo, M. and Done, C. and Dotani, T. and Ebisawa, K. and Eckart, M. and Eckert, D. and Eguchi, Satoshi and Enoto, T. and Ezoe, Y. and Foster, A. and Fujimoto, R. and Fujita, Y. and Fukazawa, Yasushi and Fukushima, Kotaro and Furuzawa, A. and Gallo, L. and García, Javier A. and Goto, E. and Gu, Liyi and Guainazzi, M. and Hagino, Kouichi and Hamaguchi, Kenji and Hatsukade, I. and Hayashi, K. and Hayashi, T. and Hell, N. and Hodges-Kluck, E. and Hornschemeier, A. and Ichinohe, Y. and Inoue, Shun and Ishi, D. and Ishida, Manabu and Ishihara, Yukiko and Ishikawa, K. and Ishisaki, Y. and Junqueira, F. and Kaastra, J. and Kallman, T. and Kanemaru, Y. and Kara, Erin and Katsuda, S. and Kelley, R. and Kilbourne, C. and Kitamoto, S. and Kobayashi, S. and Kohmura, T. and Kubota, A. and Leutenegger, M. and Loewenstein, Michael and Maeda, Yoshitomo and Markevitch, M. and Matsumoto, Hironori and Matsushita, K. and McCammon, D. and McNamara, Brian and Mernier, F. and Meulen, B. V. and Miller, E. and Miller, Jon M. and Mitsuishi, I. and Miyamoto, Asca and Mizumoto, M. and Mizuno, T. and Mori, K. and Mukai, K. and Murakami, Hiroshi and Mushotzky, R. and Nakajima, H. and Nakazawa, K. and Ness, J. and Nobukawa, K. and Nobukawa, M. and Noda, H. and Odaka, H. and Ogawa, S. and Ogorzałek, A. and Okajima, T. and Ota, Naomi and Paltani, S. and Petre, R. and Plucinsky, P. and Porter, F. and Pottschmidt, K. and Sato, Kosuke and Sato, Toshiki and Sawada, Makoto and Seta, H. and Shidatsu, M. and Simionescu, A. and Smith, Randall and Suzuki, Hiromasa and Szymkowiak, A. and Takahashi, Hiromitsu and Takeo, M. and Tamagawa, T. and Tamura, Keisuke and Tanaka, Takaaki and Tanimoto, A. and Tashiro, M. and Terada, Y. and Terashima, Y. and Tsuboi, Y. and Tsujimoto, M. and Tsunemi, H. and Tsuru, T. and Tumer, Aysegul and Uchida, Hiroyuki and Uchida, N. and Uchida, Y. and Uchiyama, H. and Ueda, S. and Ueda, Y. and Uno, S. and Vink, J. and Watanabe, S. and Williams, Brian J. and Yamada, Satoshi and Yamada, S. and Yamaguchi, Hiroya and Yamaoka, K. and Yamasaki, N. and Yamauchi, M. and Yamauchi, S. and Yaqoob, T. and Yoneyama, T. and Yoshida, Tessei and Yukita, M. and Zhuravleva, I.}
}

Abstract

The supermassive binary system, $\eta$ Carinae, is experiencing enormous wind-driven mass loss at a rate unparalleled in the rest of the Galaxy. Their wind-wind collision (WWC) continuously produces shock heated, X-ray emitting plasmas. The XRISM X-ray observatory observed the system in 2023 and 2024 when the X-ray emission began to increase toward periastron passage in 2025. This manuscript reports unprecedentedly high-resolution X-ray spectra in the iron K$\alpha$ band between 6.2 and 7.1 keV, obtained with the Resolve X-ray microcalorimeter. The hydrogen-like (Ly$\alpha$) and helium-like (He$\alpha$) lines reveal three velocity components. Two of them are broadened with maximum velocities of 2000-3000 km/s, likely originating from the post-shock companion wind. The other is relatively narrow, with a Gaussian broadening of only ~290 km/s in 1 sigma, which may originate from the post-shock companion wind at the WWC stagnation point or penetrating the primary wind. The iron fluorescent lines exhibit a moderate blueshift and broadening with velocities at 100-200 km/s, consistent with the primary wind's velocity field. The spectra also confirm a Compton shoulder of the He$\alpha$ line complex for the first time. Both fluorescing and scattering spectral profiles indicate that the binary system is seen from the companion side during these observations. The flux ratio of the Compton scattering emission to the fluorescent line suggests substantial hydrogen depletion of the primary wind, expected from CNO-cycled hydrogen nuclear fusion gas.