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

DOI: 
10.3847/1538-4357/ac8056
Publication date: 
01/08/2022
Main author: 
Ehlert S.R.
IAA authors: 
Agudo, Iván
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;Rodi, James;Jourdain, Elisabeth;Roques, Jean Pierre
Journal: 
Astrophysical Journal
Publication type: 
Article
Volume: 
935.0
Number: 
116
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 (NH ∼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.
Database: 
SCOPUS