The Astrophysical Journal Letters (Jan 2025)

Kinematic Evidence for Bipolar Ejecta Flows in the Galactic Supernova Remnant W49B

  • XRISM Collaboration,
  • Marc Audard,
  • Hisamitsu Awaki,
  • Ralf Ballhausen,
  • Aya Bamba,
  • Ehud Behar,
  • Rozenn Boissay-Malaquin,
  • Laura Brenneman,
  • Gregory V. Brown,
  • Lia Corrales,
  • Elisa Costantini,
  • Renata Cumbee,
  • María Díaz 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 L. Kelley,
  • Caroline A. Kilbourne,
  • Shunji Kitamoto,
  • Shogo Kobayashi,
  • Takayoshi Kohmura,
  • Aya Kubota,
  • Maurice A. 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 Ogorzalek,
  • Takashi Okajima,
  • Naomi Ota,
  • Stephane Paltani,
  • Robert Petre,
  • Paul Plucinsky,
  • Frederick S. Porter,
  • Katja Pottschmidt,
  • Hidetoshi Sano,
  • 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 G. Tsuru,
  • Ayşegül Tümer,
  • Hiroyuki Uchida,
  • Nagomi Uchida,
  • Yuusuke Uchida,
  • Hideki Uchiyama,
  • 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,
  • Yuki Amano,
  • Amy Gall,
  • Sharon Mitrani,
  • Kaito Murakami,
  • Roi Rahin,
  • Nari Suzuki

DOI
https://doi.org/10.3847/2041-8213/ade138
Journal volume & issue
Vol. 988, no. 2
p. L58

Abstract

Read online

W49B is a unique Galactic supernova remnant with centrally peaked, “bar”-like ejecta distribution, which was once considered evidence for a hypernova origin that resulted in a bipolar ejection of the stellar core. However, chemical abundance measurements contradict this interpretation. Closely connected to the morphology of the ejecta is its velocity distribution, which provides critical details for understanding the explosion mechanism. We report the first ever observational constraint on the kinematics of the ejecta in W49B using the Resolve microcalorimeter spectrometer on the X-ray Imaging and Spectroscopy Mission (XRISM). Using XRISM/Resolve, we measured the line-of-sight velocity traced by the Fe He α emission, which is the brightest feature in the Resolve spectrum, to vary by ±300 km s ^−1 with a smooth east-to-west gradient of a few tens of kilometers per second per parsec along the major axis. Similar trends in the line-of-sight velocity structure were found for other Fe-group elements Cr and Mn, traced by the He α emission, and also for intermediate-mass elements Si, S, Ar, and Ca, traced by the Ly α emission. The discovery of the east–west gradient in the line-of-sight velocity, together with the absence of a twin-peaked line profile or enhanced broadening in the central region, clearly rejects the equatorially expanding disk model. In contrast, the observed velocity structure suggests bipolar flows reminiscent of a bipolar explosion scenario. An alternative scenario would be a collimation of the ejecta by an elongated cavity sculpted by bipolar stellar winds.

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