TY - JOUR
T1 - Limits on X-Ray Polarization at the Core of Centaurus A as Observed with the Imaging X-Ray Polarimetry Explorer
AU - IXPE
AU - Ehlert, Steven R.
AU - Ferrazzoli, Riccardo
AU - Marinucci, Andrea
AU - Marshall, Herman L.
AU - Middei, Riccardo
AU - Pacciani, Luigi
AU - Perri, Matteo
AU - Petrucci, Pierre Olivier
AU - Puccetti, Simonetta
AU - Barnouin, Thibault
AU - Bianchi, Stefano
AU - Liodakis, Ioannis
AU - Madejski, Grzegorz
AU - Marin, Frédéric
AU - Marscher, Alan P.
AU - Matt, Giorgio
AU - Poutanen, Juri
AU - Wu, Kinwah
AU - Agudo, Iván
AU - Antonelli, Lucio A.
AU - Bachetti, Matteo
AU - Baldini, Luca
AU - Baumgartner, Wayne H.
AU - Bellazzini, Ronaldo
AU - Bongiorno, Stephen D.
AU - Bonino, Raffaella
AU - Brez, Alessandro
AU - Bucciantini, Niccoló
AU - Capitanio, Fiamma
AU - Castellano, Simone
AU - Cavazzuti, Elisabetta
AU - Ciprini, Stefano
AU - Costa, Enrico
AU - De Rosa, Alessandra
AU - Del Monte, Ettore
AU - Di Gesu, Laura
AU - Di Lalla, Niccoló
AU - Di Marco, Alessandro
AU - Donnarumma, Immacolata
AU - Doroshenko, Victor
AU - Dovčiak, Michal
AU - Enoto, Teruaki
AU - Evangelista, Yuri
AU - Fabiani, Sergio
AU - Garcia, Javier A.
AU - Gunji, Shuichi
AU - Hayashida, Kiyoshi
AU - Heyl, Jeremy
AU - Iwakiri, Wataru
AU - Pavlov, George G.
N1 - Publisher Copyright:
© 2022. The Author(s).
PY - 2022/8/1
Y1 - 2022/8/1
N2 - 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.
AB - 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.
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U2 - 10.3847/1538-4357/ac8056
DO - 10.3847/1538-4357/ac8056
M3 - Article
AN - SCOPUS:85138196662
SN - 0004-637X
VL - 935
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 116
ER -