Measurements of resonant scattering in the Perseus Cluster core with Hitomi SXS
Authors:   Hitomi Collaboration, Aharonian Felix , Akamatsu Hiroki , Akimoto Fumie , Allen Steven W , Angelini Lorella , Audard Marc , Awaki Hisamitsu , Axelsson Magnus , Bamba Aya , Bautz Marshall W , Blandford Roger , Brenneman Laura W , Brown Gregory V , Bulbul Esra , Cackett Edward M , Chernyakova Maria , Chiao Meng P , Coppi Paolo S , Costantini Elisa , de Plaa Jelle , de Vries Cor P , den Herder Jan-Willem , Done Chris , Dotani Tadayasu , Ebisawa Ken , Eckart Megan E , Enoto Teruaki , Ezoe Yuichiro , Fabian Andrew C , Ferrigno Carlo , Foster Adam R , Fujimoto Ryuichi , Fukazawa Yasushi , Furukawa Maki , Furuzawa Akihiro , Galeazzi Massimiliano , Gallo Luigi C , Gandhi Poshak , Giustini Margherita , Goldwurm Andrea , Gu Liyi , Guainazzi Matteo , Haba Yoshito , Hagino Kouichi , Hamaguchi Kenji , Harrus Ilana M , Hatsukade Isamu , Hayashi Katsuhiro , Hayashi Takayuki , Hayashida Kiyoshi , Hiraga Junko S , Hornschemeier Ann , Hoshino Akio , Hughes John P , Ichinohe Yuto , Iizuka Ryo , Inoue Hajime , Inoue Yoshiyuki , Ishida Manabu , Ishikawa Kumi , Ishisaki Yoshitaka , Iwai Masachika , Kaastra Jelle , Kallman Tim , Kamae Tsuneyoshi , Kataoka Jun , Katsuda Satoru , Kawai Nobuyuki , Kelley Richard L , Kilbourne Caroline A , Kitaguchi Takao , Kitamoto Shunji , Kitayama Tetsu , Kohmura Takayoshi , Kokubun Motohide , Koyama Katsuji , Koyama Shu , Kretschmar Peter , Krimm Hans A , Kubota Aya , Kunieda Hideyo , Laurent Philippe , Lee Shiu-Hang , Leutenegger Maurice A , Limousin Olivier O , Loewenstein Michael , Long Knox S , Lumb David , Madejski Greg , Maeda Yoshitomo , Maier Daniel , Makishima Kazuo , Markevitch Maxim , Matsumoto Hironori , Matsushita Kyoko , McCammon Dan , McNamara Brian R , Mehdipour Missagh , Miller Eric D , Miller Jon M , Mineshige Shin , Mitsuda Kazuhisa , Mitsuishi Ikuyuki , Miyazawa Takuya , Mizuno Tsunefumi , Mori Hideyuki , Mori Koji , Mukai Koji , Murakami Hiroshi , Mushotzky Richard F , Nakagawa Takao , Nakajima Hiroshi , Nakamori Takeshi , Nakashima Shinya , Nakazawa Kazuhiro , Nobukawa Kumiko K , Nobukawa Masayoshi , Noda Hirofumi , Odaka Hirokazu , Ogorzalek Anna , Ohashi Takaya , Ohno Masanori , Okajima Takashi , Ota Naomi , Ozaki Masanobu , Paerels Frits , Paltani Stéphane , Petre Robert , Pinto Ciro , Porter Frederick S , Pottschmidt Katja , Reynolds Christopher S , Safi-Harb Samar , Saito Shinya , Sakai Kazuhiro , Sasaki Toru , Sato Goro , Sato Kosuke , Sato Rie , Sawada Makoto , Schartel Norbert , Serlemtsos Peter J , Seta Hiromi , Shidatsu Megumi , Simionescu Aurora , Smith Randall K , Soong Yang , Stawarz Łukasz , Sugawara Yasuharu , Sugita Satoshi , Szymkowiak Andrew , Tajima Hiroyasu , Takahashi Hiromitsu , Takahashi Tadayuki , Takeda Shiníchiro , Takei Yoh , Tamagawa Toru , Tamura Takayuki , Tanaka Takaaki , Tanaka Yasuo , Tanaka Yasuyuki T , Tashiro Makoto S , Tawara Yuzuru , Terada Yukikatsu , Terashima Yuichi , Tombesi Francesco , Tomida Hiroshi , Tsuboi Yohko , Tsujimoto Masahiro , Tsunemi Hiroshi , Tsuru Takeshi Go , Uchida Hiroyuki , Uchiyama Hideki , Uchiyama Yasunobu , Ueda Shutaro , Ueda Yoshihiro , Uno Shiníchiro , Urry C Megan , Ursino Eugenio , Watanabe Shin , Werner Norbert , Wilkins Dan R , Williams Brian J , Yamada Shinya , Yamaguchi Hiroya , Yamaoka Kazutaka , Yamasaki Noriko Y , Yamauchi Makoto , Yamauchi Shigeo , Yaqoob Tahir , Yatsu Yoichi , Yonetoku Daisuke , Zhuravleva Irina , Zoghbi Abderahmen 
Published: January 2018

Abstract
Thanks to its high spectral resolution (∼5 eV at 6 keV), the Soft X-ray Spectrometer (SXS) on board Hitomi enables us to measure the detailed structure of spatially resolved emission lines from highly ionized ions in galaxy clusters for the first time. In this series of papers, using the SXS we have measured the velocities of gas motions, metallicities and the multi-temperature structure of the gas in the core of the Perseus Cluster. Here, we show that when inferring physical properties from line emissivities in systems like Perseus, the resonant scattering effect should be taken into account. In the Hitomi waveband, resonant scattering mostly affects the Fe xxv Heα line (w)—the strongest line in the spectrum. The flux measured by Hitomi in this line is suppressed by a factor of ∼1.3 in the inner ∼30 kpc, compared to predictions for an optically thin plasma; the suppression decreases with the distance from the center. The w line also appears slightly broader than other lines from the same ion. The observed distortions of the w line flux, shape, and distance dependence are all consistent with the expected effect of the resonant scattering in the Perseus core. By measuring the ratio of fluxes in optically thick (w) and thin (Fe xxv forbidden, Heβ, Lyα) lines, and comparing these ratios with predictions from Monte Carlo radiative transfer simulations, the velocities of gas motions have been obtained. The results are consistent with the direct measurements of gas velocities from line broadening described elsewhere in this series, although the systematic and statistical uncertainties remain significant. Further improvements in the predictions of line emissivities in plasma models, and deeper observations with future X-ray missions offering similar or better capabilities to the Hitomi SXS, will enable resonant scattering measurements to provide powerful constraints on the amplitude and anisotropy of cluster gas motions.