arXiv · 1712.06612
Temperature Structure in the Perseus Cluster Core Observed with Hitomi
Abstract
The present paper investigates the temperature structure of the X-ray emitting plasma in the core of the Perseus cluster using the 1.8--20.0 keV data obtained with the Soft X-ray Spectrometer (SXS) onboard the Hitomi Observatory. A series of four observations were carried out, with a total effective exposure time of 338 ks and covering a central region $\sim7'$ in diameter. The SXS was operated with an energy resolution of $\sim$5 eV (full width at half maximum) at 5.9 keV. Not only fine structures of K-shell lines in He-like ions but also transitions from higher principal quantum numbers are clearly resolved from Si through Fe. This enables us to perform temperature diagnostics using the line ratios of Si, S, Ar, Ca, and Fe, and to provide the first direct measurement of the excitation temperature and ionization temperature in the Perseus cluster. The observed spectrum is roughly reproduced by a single temperature thermal plasma model in collisional ionization equilibrium, but detailed line ratio diagnostics reveal slight deviations from this approximation. In particular, the data exhibit an apparent trend of increasing ionization temperature with increasing atomic mass, as well as small differences between the ionization and excitation temperatures for Fe, the only element for which both temperatures can be measured. The best-fit two-temperature models suggest a combination of 3 and 5 keV gas, which is consistent with the idea that the observed small deviations from a single temperature approximation are due to the effects of projection of the known radial temperature gradient in the cluster core along the line of sight. Comparison with the Chandra/ACIS and the XMM-Newton/RGS results on the other hand suggests that additional lower-temperature components are present in the ICM but not detectable by Hitomi SXS given its 1.8--20 keV energy band.
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Hitomi Collaboration, Felix Aharonian, Hiroki Akamatsu, Fumie Akimoto, Steven W. Allen, Lorella Angelini, Marc Audard, Hisamitsu Awaki, Magnus Axelsson, Aya Bamba, Marshall W. Bautz, Roger Blandford, Laura W. Brenneman, Gregory V. Brown, Esra Bulbul, Edward M. Cackett, Maria Chernyakova, Meng P. Chiao, Paolo S. Coppi, Elisa Costantini, Jelle de Plaa, Cor P. de Vries, Jan-Willem den Herder, Chris Done, Tadayasu Dotani, Ken Ebisawa, Megan E. Eckart, Teruaki Enoto, Yuichiro Ezoe, Andrew C. Fabian, Carlo Ferrigno, Adam R. Foster, Ryuichi Fujimoto, Yasushi Fukazawa, Maki Furukawa, Akihiro Furuzawa, Massimiliano Galeazzi, Luigi C. Gallo, Poshak Gandhi, Margherita Giustini, Andrea Goldwurm, Liyi Gu, Matteo Guainazzi, Yoshito Haba, Kouichi Hagino, Kenji Hamaguchi, Ilana M. Harrus, Isamu Hatsukade, Katsuhiro Hayashi, Takayuki Hayashi, Kiyoshi Hayashida, Junko S. Hiraga, Ann Hornschemeier, Akio Hoshino, John P. Hughes, Yuto Ichinohe, Ryo Iizuka, Hajime Inoue, Yoshiyuki Inoue, Manabu Ishida, Kumi Ishikawa, Yoshitaka Ishisaki, Masachika Iwai, Jelle Kaastra, Tim Kallman, Tsuneyoshi Kamae, Jun Kataoka, Yuichi Kato, Satoru Katsuda, Nobuyuki Kawai, Richard L. Kelley, Caroline A. Kilbourne, Takao Kitaguchi, Shunji Kitamoto, Tetsu Kitayama, Takayoshi Kohmura, Motohide Kokubun, Katsuji Koyama, Shu Koyama, Peter Kretschmar, Hans A. Krimm, Aya Kubota, Hideyo Kunieda, Philippe Laurent, Shiu-Hang Lee, Maurice A. Leutenegger, Olivier Limousin, Michael Loewenstein, Knox S. Long, David Lumb, Greg Madejski, Yoshitomo Maeda, Daniel Maier, Kazuo Makishima, Maxim Markevitch, Hironori Matsumoto, Kyoko Matsushita, Dan McCammon, Brian R. McNamara, Missagh Mehdipour. 2017-12-18. Temperature Structure in the Perseus Cluster Core Observed with Hitomi. https://doi.org/10.1093/pasj%2Fpsy004
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