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X-Ray Polarization Detection of Cassiopeia A with IXPE

Jacco Vink Dmitry Prokhorov Riccardo Ferrazzoli Patrick Slane Ping Zhou Kazunori Asakura Luca Baldini Niccoló Bucciantini Enrico Costa Alessandro Di Marco Jeremy Heyl Frédéric Marin 1 Tsunefumi Mizuno C. -Y. Ng Melissa Pesce-Rollins Brian D. Ramsey John Rankin Ajay Ratheesh Carmelo Sgró Paolo Soffitta Douglas A. Swartz Toru Tamagawa Martin C. Weisskopf Yi-Jung Yang Ronaldo Bellazzini Raffaella Bonino Elisabetta Cavazzuti Luigi Costamante Niccoló Di Lalla Luca Latronico Simone Maldera Alberto Manfreda Francesco Massaro Ikuyuki Mitsuishi Nicola Omodei Chiara Oppedisano Silvia Zane Ivan Agudo Lucio A. Antonelli Matteo Bachetti Wayne H. Baumgartner Stefano Bianchi Stephen D. Bongiorno Alessandro Brez Fiamma Capitanio Simone Castellano Stefano Ciprini Alessandra De Rosa Ettore del Monte Laura Di Gesu Immacolata Donnarumma Victor Doroshenko Michal Dovčiak Steven R. Ehlert Teruaki Enoto Yuri Evangelista Sergio Fabiani Javier A. Garcia Shuichi Gunji Kiyoshi Hayashida Wataru Iwakiri Svetlana G. Jorstad Vladimir Karas Takao Kitaguchi Jeffery J. Kolodziejczak Henric Krawczynski Fabio La Monaca Ioannis Liodakis Andrea Marinucci Alan P. Marscher Herman L. Marshall Giorgio Matt Fabio Muleri Stephen L. O'Dell Alessandro Papitto George G. Pavlov Abel L. Peirson Matteo Perri Maura Pilia Andrea Possenti Juri Poutanen Simonetta Puccetti Roger W. Romani Gloria Spandre Fabrizio Tavecchio Roberto Taverna Yuzuru Tawara Allyn F. Tennant Nicolas E. Thomas Francesco Tombesi Alessio Trois Sergey Tsygankov Roberto Turolla Kinwah Wu Fei Xie 
Abstract : We report on a ~5σ detection of polarized 3-6 keV X-ray emission from the supernova remnant Cassiopeia A (Cas A) with the Imaging X-ray Polarimetry Explorer (IXPE). The overall polarization degree of 1.8% ± 0.3% is detected by summing over a large region, assuming circular symmetry for the polarization vectors. The measurements imply an average polarization degree for the synchrotron component of ~2.5%, and close to 5% for the X-ray synchrotron-dominated forward shock region. These numbers are based on an assessment of the thermal and nonthermal radiation contributions, for which we used a detailed spatial-spectral model based on Chandra X-ray data. A pixel-by-pixel search for polarization provides a few tentative detections from discrete regions at the ~ 3σ confidence level. Given the number of pixels, the significance is insufficient to claim a detection for individual pixels, but implies considerable turbulence on scales smaller than the angular resolution. Cas A's X-ray continuum emission is dominated by synchrotron radiation from regions within ≲1017 cm of the forward and reverse shocks. We find that (i) the measured polarization angle corresponds to a radially oriented magnetic field, similar to what has been inferred from radio observations; (ii) the X-ray polarization degree is lower than in the radio band (~5%). Since shock compression should impose a tangential magnetic-field structure, the IXPE results imply that magnetic fields are reoriented within ~1017 cm of the shock. If the magnetic-field alignment is due to locally enhanced acceleration near quasi-parallel shocks, the preferred X-ray polarization angle suggests a size of 3 × 1016 cm for cells with radial magnetic fields.
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https://hal-insu.archives-ouvertes.fr/insu-03822787
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Submitted on : Thursday, October 20, 2022 - 4:06:40 PM
Last modification on : Friday, October 21, 2022 - 3:40:57 AM

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Jacco Vink, Dmitry Prokhorov, Riccardo Ferrazzoli, Patrick Slane, Ping Zhou, et al.. X-Ray Polarization Detection of Cassiopeia A with IXPE. The Astrophysical Journal, 2022, 938, ⟨10.3847/1538-4357/ac8b7b⟩. ⟨insu-03822787⟩

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