Limits on X-ray polarization at the core of Centaurus A as observed with the imaging X-Ray polarimetry explorer
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Published version
Date
2022-08-01
Authors
Ehlert, Steven R.
Ferrazzoli, Riccardo
Marinucci, Andrea
Marshall, Herman L.
Middei, Riccardo
Pacciani, Luigi
Perri, Matteo
Petrucci, Pierre-Olivier
Puccetti, Simonetta
Barnouin, Thibault
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OA Version
Published version
Citation
S.R. Ehlert, R. Ferrazzoli, A. Marinucci, H.L. Marshall, R. Middei, L. Pacciani, M. Perri, P.-O. Petrucci, S. Puccetti, T. Barnouin, S. Bianchi, I. Liodakis, G. Madejski, F. Marin, A.P. Marscher, G. Matt, J. Poutanen, K. Wu, I. Agudo, L.A. Antonelli, M. Bachetti, L. Baldini, W.H. Baumgartner, R. Bellazzini, S.D. Bongiorno, R. Bonino, A. Brez, N. Bucciantini, F. Capitanio, S. Castellano, E. Cavazzuti, S. Ciprini, E. Costa, A. De Rosa, E. Del Monte, L. Di Gesu, N. Di Lalla, A. Di Marco, I. Donnarumma, V. Doroshenko, M. Dovčiak, T. Enoto, Y. Evangelista, S. Fabiani, J.A. Garcia, S. Gunji, K. Hayashida, J. Heyl, W. Iwakiri, S.G. Jorstad, V. Karas, T. Kitaguchi, J.J. Kolodziejczak, H. Krawczynski, F. La Monaca, L. Latronico, S. Maldera, A. Manfreda, F. Massaro, I. Mitsuishi, T. Mizuno, F. Muleri, M. Negro, C.-Y. Ng, S.L. O’Dell, N. Omodei, C. Oppedisano, A. Papitto, G.G. Pavlov, A.L. Peirson, M. Pesce-Rollins, M. Pilia, A. Possenti, B.D. Ramsey, J. Rankin, A. Ratheesh, R.W. Romani, C. Sgrò, P. Slane, P. Soffitta, G. Spandre, T. Tamagawa, F. Tavecchio, R. Taverna, Y. Tawara, A.F. Tennant, N.E. Thomas, F. Tombesi, A. Trois, S. Tsygankov, R. Turolla, J. Vink, M.C. Weisskopf, F. Xie, S. Zane, J. Rodi, E. Jourdain, J.-P. Roques. 2022. "Limits on X-Ray Polarization at the Core of Centaurus A as Observed with the Imaging X-Ray Polarimetry Explorer" The Astrophysical Journal: an international review of astronomy and astronomical physics, Volume 935, Issue 2, pp.116-116. https://doi.org/10.3847/1538-4357/ac8056
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.
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© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.