Hitomi X-ray observation of the pulsar wind nebula G21.5−0.9
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 , 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 , 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 , 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 Shin’ichiro , 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 Shin’ichiro , 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 , Sato Toshiki , Nakaniwa Nozomu , Murakami Hiroaki , Guest Benson 
Published: March 2018

Abstract
We present results from the Hitomi X-ray observation of a young composite-type supernova remnant (SNR) G21.5−0.9, whose emission is dominated by the pulsar wind nebula (PWN) contribution. The X-ray spectra in the 0.8–80 keV range obtained with the Soft X-ray Spectrometer (SXS), Soft X-ray Imager, and Hard X-ray Imager (HXI) show a significant break in the continuum as previously found with the NuSTAR observation. After taking into account all known emissions from the SNR other than the PWN itself, we find that the Hitomi spectra can be fitted with a broken power law with photon indices of Γ1 = 1.74 ± 0.02 and Γ2 = 2.14 ± 0.01 below and above the break at 7.1 ± 0.3 keV, which is significantly lower than the NuSTAR result (∼9.0 keV). The spectral break cannot be reproduced by time-dependent particle injection one-zone spectral energy distribution models, which strongly indicates that a more complex emission model is needed, as suggested by recent theoretical models. We also search for narrow emission or absorption lines with the SXS, and perform a timing analysis of PSR J1833−1034 with the HXI and the Soft Gamma-ray Detector. No significant pulsation is found from the pulsar. However, unexpectedly, narrow absorption line features are detected in the SXS data at 4.2345 keV and 9.296 keV with a significance of 3.65 σ. While the origin of these features is not understood, their mere detection opens up a new field of research and was only possible with the high resolution, sensitivity, and ability to measure extended sources provided by an X-ray microcalorimeter.