Limits on X-Ray Polarization at the Core of Centaurus A as Observed with the Imaging X-Ray Polarimetry Explorer
Articolo
Data di Pubblicazione:
2022
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.
Tipologia CRIS:
03A-Articolo su Rivista
Elenco autori:
Ehlert S.R.; Ferrazzoli R.; Marinucci A.; Marshall H.L.; Middei R.; Pacciani L.; Perri M.; Petrucci P.-O.; Puccetti S.; Barnouin T.; Bianchi S.; Liodakis I.; Madejski G.; Marin F.; Marscher A.P.; Matt G.; Poutanen J.; Wu K.; Agudo I.; Antonelli L.A.; Bachetti M.; Baldini L.; Baumgartner W.H.; Bellazzini R.; Bongiorno S.D.; 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 J.A.; Gunji S.; Hayashida K.; Heyl J.; Iwakiri W.; Jorstad S.G.; Karas V.; Kitaguchi T.; Kolodziejczak J.J.; Krawczynski H.; La Monaca F.; Latronico L.; Maldera S.; Manfreda A.; Massaro F.; Mitsuishi I.; Mizuno T.; Muleri F.; Negro M.; Ng C.-Y.; O'dell S.L.; Omodei N.; Oppedisano C.; Papitto A.; Pavlov G.G.; Peirson A.L.; Pesce-Rollins M.; Pilia M.; Possenti A.; Ramsey B.D.; Rankin J.; Ratheesh A.; Romani R.W.; Sgro C.; Slane P.; Soffitta P.; Spandre G.; Tamagawa T.; Tavecchio F.; Taverna R.; Tawara Y.; Tennant A.F.; Thomas N.E.; Tombesi F.; Trois A.; Tsygankov S.; Turolla R.; Vink J.; Weisskopf M.C.; Xie F.; Zane S.; Rodi J.; Jourdain E.; Roques J.-P.
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