Refereed journal article or data article (A1)
Limits on X-Ray Polarization at the Core of Centaurus A as Observed with the Imaging X-Ray Polarimetry Explorer
List of Authors: Ehlert SR, Ferrazzoli R, Marinucci A, Marshall HL, Middei R, Pacciani L, Perri M, Petrucci PO, Puccetti S, Barnouin T, Bianchi S, Liodakis I, Madejski G, Marin F, Marscher AP, Matt G, Poutanen J, Wu K, Agudo I, Antonelli LA, Bachetti M, Baldini L, Baumgartner WH, Bellazzini R, Bongiorno SD, Bonino R, Brez A, Bucciantini N, Capitanio F, Castellano S, Cavazzuti E, Ciprini S, Costa E, De Rosa A, Del Monte E, Di Gesu L, Di Lalla N, Di Marco A, Donnarumma I, Doroshenko V, Dovciak M, Enoto T, Evangelista Y, Fabiani S, Garcia JA, Gunji S, Hayashida K, Heyl J, Iwakiri W, Jorstad SG, Karas V, Kitaguchi T, Kolodziejczak JJ, Krawczynski H, La Monaca F, Latronico L, Maldera S, Manfreda A, Massaro F, Mitsuishi I, Mizuno T, Muleri F, Negro M, Ng CY, O'Dell SL, Omodei N, Oppedisano C, Papitto A, Pavlov GG, Peirson AL, Pesce-Rollins M, Pilia M, Possenti A, Ramsey BD, Rankin J, Ratheesh A, Romani RW, Sgro C, Slane P, Soffitta P, Spandre G, Tamagawa T, Tavecchio F, Taverna R, Tawara Y, Tennant AF, Thomas NE, Tombesi F, Trois A, Tsygankov S, Turolla R, Vink J, Weisskopf MC, Xie F, Zane S, Rodi J, Jourdain E, Roques JP
Publisher: IOP Publishing Ltd
Publication year: 2022
Journal: Astrophysical Journal
Journal name in source: ASTROPHYSICAL JOURNAL
Journal acronym: ASTROPHYS J
Volume number: 935
Issue number: 2
Number of pages: 10
ISSN: 0004-637X
eISSN: 1538-4357
DOI: http://dx.doi.org/10.3847/1538-4357/ac8056
URL: https://iopscience.iop.org/article/10.3847/1538-4357/ac8056
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/176536414
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 psi 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) similar to 10(23) cm(-2)) and a Fe K alpha 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 alpha 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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