A1 Refereed original research article in a scientific journal
Limits on X-Ray Polarization at the Core of Centaurus A as Observed with the Imaging X-Ray Polarimetry Explorer
Authors: Ehlert Steven R., Ferrazzoli Riccardo, Marinucci Andrea, Marshall Herman L., Middei Riccardo, Pacciani Luigi, Perri Matteo, Petrucci Pierre-Olivier, Puccetti Simonetta, Barnouin Thibault, Bianchi Stefano, Liodakis Ioannis, Madejski Grzegorz, Marin Frédéric, Marscher Alan P., Matt Giorgio, Poutanen Juri, Wu Kinwah, Agudo Iván, Antonelli Lucio A., Bachetti Matteo, Baldini Luca, Baumgartner Wayne H., Bellazzini Ronaldo, Bongiorno Stephen D., Bonino Raffaella, Brez Alessandro, Bucciantini Niccoló, Capitanio Fiamma, Castellano Simone, Cavazzuti Elisabetta, Ciprini Stefano, Costa Enrico, De Rosa Alessandra, Del Monte Ettore, Di Gesu Laura, Di Lalla Niccoló, Di Marco Alessandro, Donnarumma Immacolata, Doroshenko Victor, Dovčiak Michal, Enoto Teruaki, Evangelista Yuri, Fabiani Sergio, Garcia Javier A., Gunji Shuichi, Hayashida Kiyoshi, Heyl Jeremy, Iwakiri Wataru, Jorstad Svetlana G., Karas Vladimir, Kitaguchi Takao, Kolodziejczak Jeffery J., Krawczynski Henric, La Monaca Fabio, Latronico Luca, Maldera Simone, Manfreda Alberto, Massaro Francesco, Mitsuishi Ikuyuki, Mizuno Tsunefumi, Muleri Fabio, Negro Michela, Ng C.-Y., O'Dell Stephen L., Omodei Nicola, Oppedisano Chiara, Papitto Alessandro, Pavlov George G., Peirson Abel L., Pesce-Rollins Melissa, Pilia Maura, Possenti Andrea, Ramsey Brian D., Rankin John, Ratheesh Ajay, Romani Roger W., Sgrò Carmelo, Slane Patrick, Soffitta Paolo, Spandre Gloria, Tamagawa Toru, Tavecchio Fabrizio, Taverna Roberto, Tawara Yuzuru, Tennant Allyn F., Thomas Nicholas E., Tombesi Francesco, Trois Alessio, Tsygankov Sergey, Turolla Roberto, Vink Jacco, Weisskopf Martin C., Xie Fei, Zane Silvia, (IXPE Collaboration), Rodi James, Jourdain Elisabeth, Roques Jean-Pierre
Publisher: IOP Publishing Ltd
Publication year: 2022
Journal: Astrophysical Journal
Journal name in source: ASTROPHYSICAL JOURNAL
Journal acronym: ASTROPHYS J
Article number: 116
Volume: 935
Issue: 2
Number of pages: 10
ISSN: 0004-637X
eISSN: 1538-4357
DOI: https://doi.org/10.3847/1538-4357/ac8056(external)
Web address : https://iopscience.iop.org/article/10.3847/1538-4357/ac8056(external)
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/176536414(external)
We present measurements of the polarization of X-rays in the 2-8 keV band from the nucleus of the radio galaxy Centaurus A (Cen A), using a 100 ks observation from the Imaging X-ray Polarimetry Explorer (IXPE). Nearly simultaneous observations of Cen A were also taken with the Swift, NuSTAR, and INTEGRAL observatories. No statistically significant degree of polarization is detected with IXPE. These observations have a minimum detectable polarization at 99% confidence (MDP99) of 6.5% using a weighted, spectral model-independent calculation in the 2-8 keV band. The polarization angle psi is consequently unconstrained. Spectral fitting across three orders of magnitude in X-ray energy (0.3-400 keV) demonstrates that the SED of Cen A is well described by a simple power law with moderate intrinsic absorption (N (H) similar to 10(23) cm(-2)) and a Fe K alpha emission line, although a second unabsorbed power law is required to account for the observed spectrum at energies below 2 keV. This spectrum suggests that the reprocessing material responsible for this emission line is optically thin and distant from the central black hole. Our upper limits on the X-ray polarization are consistent with the predictions of Compton scattering, although the specific seed photon population responsible for the production of the X-rays cannot be identified. The low polarization degree, variability in the core emission, and the relative lack of variability in the Fe K alpha emission line support a picture where electrons are accelerated in a region of highly disordered magnetic fields surrounding the innermost jet.
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