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

1 ObAS - Observatoire astronomique de Strasbourg

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.

Domaines: Planète et Univers [physics]

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, 2022, 935 (2), pp.116. ⟨10.3847/1538-4357/ac8056⟩. ⟨insu-03763401⟩