Limits on X-Ray Polarization at the Core of Centaurus A as Observed with the Imaging X-Ray Polarimetry Explorer
Journal
Date Issued
2022
Author(s)
Ehlert, Steven R.
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Marinucci, Andrea
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Marshall, Herman L.
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Petrucci, Pierre-Olivier
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Puccetti, Simonetta
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Barnouin, Thibault
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Bianchi, Stefano
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Liodakis, Ioannis
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Madejski, Grzegorz
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Marin, Frédéric
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Marscher, Alan P.
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Poutanen, Juri
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Wu, Kinwah
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Agudo, Iván
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Baldini, Luca
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Baumgartner, Wayne H.
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Bellazzini, Ronaldo
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Bongiorno, Stephen D.
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Bonino, Raffaella
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Brez, Alessandro
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Castellano, Simone
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Cavazzuti, Elisabetta
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Ciprini, Stefano
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Di Gesu, Laura
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Di Lalla, Niccoló
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Donnarumma, Immacolata
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Doroshenko, Victor
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Dovčiak, Michal
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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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Heyl, Jeremy
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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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Latronico, Luca
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Maldera, Simone
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Manfreda, Alberto
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Mitsuishi, Ikuyuki
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Mizuno, Tsunefumi
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Negro, Michela
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Ng, C. -Y.
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O'Dell, Stephen L.
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Omodei, Nicola
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Oppedisano, Chiara
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Pavlov, George G.
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Peirson, Abel L.
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Pesce-Rollins, Melissa
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Ramsey, Brian D.
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Romani, Roger W.
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Sgrò, Carmelo
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Slane, Patrick
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Spandre, Gloria
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Tamagawa, Toru
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Taverna, Roberto
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Tawara, Yuzuru
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Tennant, Allyn F.
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Thomas, Nicholas E.
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Tsygankov, Sergey
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Turolla, Roberto
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Vink, Jacco
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Weisskopf, Martin C.
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Zane, Silvia
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IXPE Collaboration
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Jourdain, Elisabeth
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Roques, Jean-Pierre
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 (MDP99) 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 ~ 1023 cm-2) and a Fe Kα 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 Kα emission line support a picture where electrons are accelerated in a region of highly disordered magnetic fields surrounding the innermost jet....
Volume
935
Issue
2
Start page
116
Issn Identifier
0004-637X
Rights
open.access
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