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Limits on X-Ray Polarization at the Core of Centaurus A as Observed with the Imaging X-Ray Polarimetry Explorer

Steven Ehlert Riccardo Ferrazzoli Andrea Marinucci Herman Marshall Riccardo Middei Luigi Pacciani Matteo Perri Pierre-Olivier Petrucci Simonetta Puccetti Thibault Barnouin 1 Stefano Bianchi Ioannis Liodakis Grzegorz Madejski Frédéric Marin 1 Alan Marscher Giorgio Matt Juri Poutanen Kinwah Wu Iván Agudo Lucio Antonelli Matteo Bachetti Luca Baldini Wayne Baumgartner Ronaldo Bellazzini Stephen Bongiorno Raffaella Bonino Alessandro Brez Niccoló Bucciantini Fiamma Capitanio Simone Castellano Elisabetta Cavazzuti Stefano Ciprini Enrico Costa Alessandra de Rosa Ettore del Monte Laura Di Gesu Niccoló Di Lalla Alessandro Di Marco Immacolata Donnarumma Victor Doroshenko Michal Dovčiak Teruaki Enoto Yuri Evangelista Sergio Fabiani Javier Garcia Shuichi Gunji Kiyoshi Hayashida Jeremy Heyl Wataru Iwakiri Svetlana Jorstad Vladimir Karas Takao Kitaguchi Jeffery Kolodziejczak Henric Krawczynski Fabio La Monaca Luca Latronico Simone Maldera Alberto Manfreda Francesco Massaro Ikuyuki Mitsuishi Tsunefumi Mizuno Fabio Muleri Michela Negro C.-Y. Ng Stephen O’dell Nicola Omodei Chiara Oppedisano Alessandro Papitto George Pavlov Abel Peirson Melissa Pesce-Rollins Maura Pilia Andrea Possenti Brian Ramsey John Rankin Ajay Ratheesh Roger Romani Carmelo Sgrò Patrick Slane Paolo Soffitta Gloria Spandre Toru Tamagawa Fabrizio Tavecchio Roberto Taverna Yuzuru Tawara Allyn Tennant Nicholas Thomas Francesco Tombesi Alessio Trois Sergey Tsygankov Roberto Turolla Jacco Vink Martin Weisskopf Fei Xie Silvia Zane James Rodi Elisabeth Jourdain Jean-Pierre Roques 
Abstract : Abstract 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 (MDP 99 ) of 6.5% using a weighted, spectral model-independent calculation in the 2–8 keV band. The polarization angle ψ 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 ∼ 10 23 cm −2 ) and a Fe K α 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 α 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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https://hal-insu.archives-ouvertes.fr/insu-03763401
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Submitted on : Monday, August 29, 2022 - 3:56:12 PM
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Steven Ehlert, Riccardo Ferrazzoli, Andrea Marinucci, Herman Marshall, Riccardo Middei, et al.. Limits on X-Ray Polarization at the Core of Centaurus A as Observed with the Imaging X-Ray Polarimetry Explorer. The Astrophysical Journal, American Astronomical Society, 2022, 935 (2), pp.116. ⟨10.3847/1538-4357/ac8056⟩. ⟨insu-03763401⟩

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