Paper: XRISM Constraints on Unidentified X-Ray Emission Lines, Including the 3.5 keV Line, in the Stacked Spectrum of 10 Galaxy Clusters
Authors: Marc Audard, Hisamitsu Awaki, Ralf Ballhausen, Aya Bamba, Ehud Behar, Rozenn Boissay-Malaquin, Laura Brenneman, Gregory V. Brown, Lia Corrales, Elisa Costantini, Renata Cumbee, Maria Diaz Trigo, Chris Done, Tadayasu Dotani, Ken Ebisawa, Megan E. Eckart, Dominique Eckert, Satoshi Eguchi, Teruaki Enoto, Yuichiro Ezoe, Adam Foster, Ryuichi Fujimoto, Yutaka Fujita, Yasushi Fukazawa, Kotaro Fukushima, Akihiro Furuzawa, Luigi Gallo, Javier A. García, Liyi Gu, Matteo Guainazzi, Kouichi Hagino, Kenji Hamaguchi, Isamu Hatsukade, Katsuhiro Hayashi, Takayuki Hayashi, Natalie Hell, Edmund Hodges-Kluck, Ann Hornschemeier, Yuto Ichinohe, Daiki Ishi, Manabu Ishida, Kumi Ishikawa, Yoshitaka Ishisaki, Jelle Kaastra, Timothy Kallman, Erin Kara, Satoru Katsuda, Yoshiaki Kanemaru, Richard Kelley, Caroline Kilbourne, Shunji Kitamoto, Shogo Kobayashi, Takayoshi Kohmura, Aya Kubota, Maurice Leutenegger, Michael Loewenstein, Yoshitomo Maeda, Maxim Markevitch, Hironori Matsumoto, Kyoko Matsushita, Dan McCammon, Brian McNamara, François Mernier, Eric D. Miller, Jon M. Miller, Ikuyuki Mitsuishi, Misaki Mizumoto, Tsunefumi Mizuno, Koji Mori, Koji Mukai, Hiroshi Murakami, Richard Mushotzky, Hiroshi Nakajima, Kazuhiro Nakazawa, Jan-Uwe Ness, Kumiko Nobukawa, Masayoshi Nobukawa, Hirofumi Noda, Hirokazu Odaka, Shoji Ogawa, Anna Ogorzałek, Takashi Okajima, Naomi Ota, Stephane Paltani, Robert Petre, Paul Plucinsky, Frederick S. Porter, Katja Pottschmidt, Kosuke Sato, Toshiki Sato, Makoto Sawada, Hiromi Seta, Megumi Shidatsu, Aurora Simionescu, Randall Smith, Hiromasa Suzuki, Andrew Szymkowiak, Hiromitsu Takahashi, Mai Takeo, Toru Tamagawa, Keisuke Tamura, Takaaki Tanaka, Atsushi Tanimoto, Makoto Tashiro, Yukikatsu Terada, Yuichi Terashima, Yohko Tsuboi, Masahiro Tsujimoto, Hiroshi Tsunemi, Takeshi Tsuru, Ayşegül Tümer, Hiroyuki Uchida, Nagomi Uchida, Yuusuke Uchida, Hideki Uchiyama, Shutaro Ueda, Yoshihiro Ueda, Shinichiro Uno, Jacco Vink, Shin Watanabe, Brian J. Williams, Satoshi Yamada, Shinya Yamada, Hiroya Yamaguchi, Kazutaka Yamaoka, Noriko Yamasaki, Makoto Yamauchi, Shigeo Yamauchi, Tahir Yaqoob, Tomokage Yoneyama, Tessei Yoshida, Mihoko Yukita, Irina Zhuravleva, Jean-Paul Breuer, Priyanka Chakraborty, Stefano Ettori, Andrew Fabian, Annie Heinrich, Marie Kondo, Julie HLavacek-Larrondo, Hannah McCall, Paul Nulsen, Tom Rose, Helen Russell, Arnab Sarkar, Evan Scannapieco, Kazunori Suda, Ming Sun, Prathamesh Tamhane, Nhut Truong, Norbert Werner, Congyao Zhang
Figure caption: Best-fit flux for an additional line as a function of its energy across the 2.5–15 keV rest-frame band (split into three intervals for clarity). The red solid line shows the best-fit line flux for a line width of 950 km s−1, the weighted velocity dispersion expected for DM in this sample, while the red dotted lines show the 3σ range. The black solid line shows the best-fit line flux for a width of 160 km s−1 (an ICM line), while the black dotted lines show its 3σ range. The vertical gray shaded areas mark strong ICM emission lines, where the search for faint lines is not possible. The right vertical axis shows the approximate corresponding DM particle decay rate Γ, assuming all DM is comprised of the decaying particle. The green cross shows the energy range and decay rate (and 1σ error) for the B14 3.5 keV line, which is still a factor of 5 below our 3σ limit on the broad line in the same energy range. The blue dashed line shows a polynomial fit to approximate the 3σ upper bound. We also mark the positions of 6.40 keV Fe fluorescent line likely from X-ray AGN, the possible Fe charge exchange feature at ~ 8.8 keV and three bumps at E> 9.8 keV likely from residual NXB lines.