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Published October 1, 2022 | public
Journal Article

X-Ray Polarization Detection of Cassiopeia A with IXPE

Vink, Jacco ORCID icon
Prokhorov, Dmitry
Ferrazzoli, Riccardo ORCID icon
Slane, Patrick ORCID icon
Zhou, Ping ORCID icon
Asakura, Kazunori
Baldini, Luca ORCID icon
Bucciantini, Niccoló
Costa, Enrico ORCID icon
Di Marco, Alessandro ORCID icon
Heyl, Jeremy ORCID icon
Marin, Frédéric ORCID icon
Mizuno, Tsunefumi ORCID icon
Ng, C.-Y.
Pesce-Rollins, Melissa ORCID icon
Ramsey, Brian D.
Rankin, John ORCID icon
Ratheesh, Ajay
Sgró, Carmelo ORCID icon
Soffitta, Paolo ORCID icon
Swartz, Douglas A.
Tamagawa, Toru
Weisskopf, Martin C. ORCID icon
Yang, Yi-Jung
Bellazzini, Ronaldo ORCID icon
Bonino, Raffaella ORCID icon
Cavazzuti, Elisabetta ORCID icon
Costamante, Luigi
Di Lalla, Niccoló ORCID icon
Latronico, Luca ORCID icon
Maldera, Simone ORCID icon
Manfreda, Alberto ORCID icon
Massaro, Francesco ORCID icon
Mitsuishi, Ikuyuki
Omodei, Nicola ORCID icon
Oppedisano, Chiara
Zane, Silvia
Agudo, Ivan ORCID icon
Antonelli, Lucio A.
Bachetti, Matteo ORCID icon
Baumgartner, Wayne H.
Bianchi, Stefano ORCID icon
Bongiorno, Stephen D.
Brez, Alessandro
Capitanio, Fiamma ORCID icon
Castellano, Simone ORCID icon
Ciprini, Stefano ORCID icon
De Rosa, Alessandra ORCID icon
Del Monte, Ettore ORCID icon
Di Gesu, Laura
Donnarumma, Immacolata
Doroshenko, Victor ORCID icon
Dovčiak, Michal ORCID icon
Ehlert, Steven R. ORCID icon
Enoto, Teruaki ORCID icon
Evangelista, Yuri
Fabiani, Sergio ORCID icon
García, Javier A. ORCID icon
Gunji, Shuichi
Hayashida, Kiyoshi
Iwakiri, Wataru ORCID icon
Jorstad, Svetlana G. ORCID icon
Karas, Vladimir ORCID icon
Kitaguchi, Takao
Kolodziejczak, Jeffery J.
Krawczynski, Henric ORCID icon
La Monaca, Fabio ORCID icon
Liodakis, Ioannis ORCID icon
Marinucci, Andrea ORCID icon
Marscher, Alan P. ORCID icon
Marshall, Herman L. ORCID icon
Matt, Giorgio ORCID icon
Muleri, Fabio ORCID icon
O'Dell, Stephen L.
Papitto, Alessandro ORCID icon
Pavlov, George G. ORCID icon
Peirson, Abel L. ORCID icon
Perri, Matteo
Pilia, Maura ORCID icon
Possenti, Andrea ORCID icon
Poutanen, Juri ORCID icon
Puccetti, Simonetta ORCID icon
Romani, Roger W. ORCID icon
Spandre, Gloria
Tavecchio, Fabrizio ORCID icon
Taverna, Roberto
Tawara, Yuzuru
Tennant, Allyn F.
Thomas, Nicolas E.
Tombesi, Francesco ORCID icon
Trois, Alessio
Tsygankov, Sergey ORCID icon
Turolla, Roberto ORCID icon
Wu, Kinwah
Xie, Fei

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.

Additional Information

The Imaging X-ray Polarimetry Explorer (IXPE) is a joint US and Italian mission. The US contribution is supported by the National Aeronautics and Space Administration (NASA) and led and managed by its Marshall Space Flight Center (MSFC), with industry partner Ball Aerospace (contract NNM15AA18C). The Italian contribution is supported by the Italian Space Agency (Agenzia Spaziale Italiana, ASI) through contract ASI-OHBI-2017-12-I.0, agreements ASI-INAF-2017-12-H0 and ASI-INFN-2017.13-H0, and its Space Science Data Center (SSDC), and by the Istituto Nazionale di Astrofisica (INAF) and the Istituto Nazionale di Fisica Nucleare (INFN) in Italy. This research used data products provided by the IXPE Team (MSFC, SSDC, INAF, and INFN) and distributed with additional software tools by the High-Energy Astrophysics Science Archive Research Center (HEASARC), at NASA Goddard Space Flight Center (GSFC). J.V. and D.P. are supported by funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 101004131 (SHARP). The research at Boston University was supported in part by National Science Foundation grant AST-2108622. We thank Dawoon Kim for kindly providing us with his script for making polar plots of polarization degree and angle. Software: ixpeobsim (Baldini et al. 2022).

Additional details

Created:
August 22, 2023
Modified:
October 24, 2023