arXiv · 2206.06713
X-ray polarization detection of Cassiopeia A with IXPE
Abstract
We report on a $\sim 5\sigma$ detection of polarized 3-6 keV X-ray emission from the supernova remnant Cassiopeia A with the Imaging X-ray Polarimetry Explorer (IXPE). The overall polarization degree of $1.8 \pm 0.3$% 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 $\sim 2.5$%, and close to 5% for the X-ray synchrotron-domimated forward-shock region. These numbers are based on an assessment of the thermal and non-thermal 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 $\sim 3\sigma$ 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 $\lesssim 10^{17}$ 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 ($\sim 5$%). Since shock compression should impose a tangential magnetic field structure, the IXPE results imply that magnetic-fields are reoriented within $\sim 10^{17}$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 $3\times 10^{16}$ cm for cells with radial magnetic fields.
Explore related subjects
Keep this discovery
Jacco Vink, Dmitry Prokhorov, Riccardo Ferrazzoli, Patrick Slane, Ping Zhou, Kazunori Asakura, Luca Baldini, Niccolo Bucciantini, Enrico Costa, Alessandro Di Marco, Jeremy Heyl, Frederic Marin, Tsunefumi Mizuno, C. Y. Ng, Melissa Pesce-Rollins, Brian D. Ramsey, John Rankin, Ajay Ratheesh, Carmelo Sgro, Paolo Soffitta, Douglas A. Swartz, Toru Tamagawa, Martin C. Weisskopf, Yi-Jung Yang, Ronaldo Bellazzini, Raffaella Bonino, Elisabetta Cavazzuti, Luigi Costamante, Niccolo 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 Dovciak, 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. 2022-06-14. X-ray polarization detection of Cassiopeia A with IXPE. https://doi.org/10.3847/1538-4357%2Fac8b7b
Cite the original work for its findings. Save a collection to share your selection of sources.