X-Ray Polarization Detection of Cassiopeia A with IXPE

Journal
Date Issued
2022
Author(s)
Vink, Jacco
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Prokhorov, Dmitry
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Slane, Patrick
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Zhou, Ping
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Asakura, Kazunori
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Baldini, Luca
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Heyl, Jeremy
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Marin, Frédéric
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Mizuno, Tsunefumi
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Ng, C. -Y.
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Pesce-Rollins, Melissa
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Ramsey, Brian D.
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Sgró, Carmelo
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Swartz, Douglas A.
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Tamagawa, Toru
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Weisskopf, Martin C.
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Yang, Yi-Jung
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Bellazzini, Ronaldo
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Bonino, Raffaella
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Cavazzuti, Elisabetta
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Costamante, Luigi
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Di Lalla, Niccoló
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Latronico, Luca
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Maldera, Simone
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Manfreda, Alberto
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Mitsuishi, Ikuyuki
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Omodei, Nicola
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Oppedisano, Chiara
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Zane, Silvia
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Agudo, Ivan
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•
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Baumgartner, Wayne H.
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Bianchi, Stefano
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Bongiorno, Stephen D.
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Brez, Alessandro
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Castellano, Simone
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Ciprini, Stefano
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Di Gesu, Laura
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Donnarumma, Immacolata
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Doroshenko, Victor
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Dovčiak, Michal
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Ehlert, Steven R.
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Enoto, Teruaki
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Garcia, Javier A.
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Gunji, Shuichi
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Hayashida, Kiyoshi
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Iwakiri, Wataru
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Jorstad, Svetlana G.
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Karas, Vladimir
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Kitaguchi, Takao
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Kolodziejczak, Jeffery J.
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Krawczynski, Henric
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Liodakis, Ioannis
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Marinucci, Andrea
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Marscher, Alan P.
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Marshall, Herman L.
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O'Dell, Stephen L.
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Pavlov, George G.
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Peirson, Abel L.
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Poutanen, Juri
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Puccetti, Simonetta
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Romani, Roger W.
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Spandre, Gloria
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Taverna, Roberto
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Tawara, Yuzuru
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Tennant, Allyn F.
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Thomas, Nicolas E.
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Tsygankov, Sergey
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Turolla, Roberto
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Wu, Kinwah
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DOI
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....
Volume
938
Issue
1
Start page
40
Uri
Url
Issn Identifier
0004-637X
Rights
open.access
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