Vink, Jacco and Prokhorov, Dmitry and Ferrazzoli, Riccardo and Slane, Patrick and Zhou, Ping and Asakura, Kazunori and Baldini, Luca and Bucciantini, Niccoló and Costa, Enrico and Di Marco, Alessandro and Heyl, Jeremy and Marin, Frédéric and Mizuno, Tsunefumi and Ng, C.-Y. and Pesce-Rollins, Melissa and Ramsey, Brian D. and Rankin, John and Ratheesh, Ajay and Sgró, Carmelo and Soffitta, Paolo and Swartz, Douglas A. and Tamagawa, Toru and Weisskopf, Martin C. and Yang, Yi-Jung and Bellazzini, Ronaldo and Bonino, Raffaella and Cavazzuti, Elisabetta and Costamante, Luigi and Di Lalla, Niccoló and Latronico, Luca and Maldera, Simone and Manfreda, Alberto and Massaro, Francesco and Mitsuishi, Ikuyuki and Omodei, Nicola and Oppedisano, Chiara and Zane, Silvia and Agudo, Ivan and Antonelli, Lucio A. and Bachetti, Matteo and Baumgartner, Wayne H. and Bianchi, Stefano and Bongiorno, Stephen D. and Brez, Alessandro and Capitanio, Fiamma and Castellano, Simone and Ciprini, Stefano and De Rosa, Alessandra and Del Monte, Ettore and Di Gesu, Laura and Donnarumma, Immacolata and Doroshenko, Victor and Dovčiak, Michal and Ehlert, Steven R. and Enoto, Teruaki and Evangelista, Yuri and Fabiani, Sergio and García, Javier A. and Gunji, Shuichi and Hayashida, Kiyoshi and Iwakiri, Wataru and Jorstad, Svetlana G. and Karas, Vladimir and Kitaguchi, Takao and Kolodziejczak, Jeffery J. and Krawczynski, Henric and La Monaca, Fabio and Liodakis, Ioannis and Marinucci, Andrea and Marscher, Alan P. and Marshall, Herman L. and Matt, Giorgio and Muleri, Fabio and O'Dell, Stephen L. and Papitto, Alessandro and Pavlov, George G. and Peirson, Abel L. and Perri, Matteo and Pilia, Maura and Possenti, Andrea and Poutanen, Juri and Puccetti, Simonetta and Romani, Roger W. and Spandre, Gloria and Tavecchio, Fabrizio and Taverna, Roberto and Tawara, Yuzuru and Tennant, Allyn F. and Thomas, Nicolas E. and Tombesi, Francesco and Trois, Alessio and Tsygankov, Sergey and Turolla, Roberto and Wu, Kinwah and Xie, Fei (2022) X-Ray Polarization Detection of Cassiopeia A with IXPE. Astrophysical Journal, 938 (1). Art. No. 40. ISSN 0004-637X. doi:10.3847/1538-4357/ac8b7b. https://resolver.caltech.edu/CaltechAUTHORS:20221021-259555500.14
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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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| 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). | ||||||||||||||||||
| Group: | Space Radiation Laboratory | ||||||||||||||||||
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| Issue or Number: | 1 | ||||||||||||||||||
| DOI: | 10.3847/1538-4357/ac8b7b | ||||||||||||||||||
| Record Number: | CaltechAUTHORS:20221021-259555500.14 | ||||||||||||||||||
| Persistent URL: | https://resolver.caltech.edu/CaltechAUTHORS:20221021-259555500.14 | ||||||||||||||||||
| Usage Policy: | No commercial reproduction, distribution, display or performance rights in this work are provided. | ||||||||||||||||||
| ID Code: | 117529 | ||||||||||||||||||
| Collection: | CaltechAUTHORS | ||||||||||||||||||
| Deposited By: | Research Services Depository | ||||||||||||||||||
| Deposited On: | 27 Oct 2022 20:47 | ||||||||||||||||||
| Last Modified: | 27 Oct 2022 20:47 |
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