X-ray polarization measurement of the gold standard of radio-quiet active galactic nuclei: NGC 1068
Marin, F.; Marinucci, A.; Laurenti, M.; Kim, D. E.; Barnouin, T.; Di Marco, A.; Ursini, F.; Bianchi, S.; Ravi, S.; Marshall, H. L.; Matt, G.; Chen, C.-T.; Gianolli, V. E.; Ingram, A.; Middei, R.; Maksym, W. P.; Panagiotou, C.; Podgorny, J.; Puccetti, S.; Ratheesh, A.; Tombesi, F.; Agudo, I.; Antonelli, L. A.; Bachetti, M.; Baldini, L.; Baumgartner, W.; Bellazzini, R.; Bongiorno, S.; 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.; Donnarumma, I.; Doroshenko, V.; Dovčiak, M.; Ehlert, S.; Enoto, T.; Evangelista, Y.; Fabiani, S.; Ferrazzoli, R.; Garcia, J.; Gunji, S.; Heyl, J.; Iwakiri, W.; Jorstad, S.; Kaaret, P.; Karas, V.; Kislat, F.; Kitaguchi, T.; Kolodziejczak, J.; Krawczynski, H.; La Monaca, F.; Latronico, L.; Liodakis, I.; Madejski, G.; Maldera, S.; Manfreda, A.; Marscher, A.; Massaro, F.; Mitsuishi, I.; Mizuno, T.; Muleri, F.; Negro, M.; Ng, S.; O’Dell, S.; Omodei, N.; Oppedisano, C.; Papitto, A.; Pavlov, G.; Perri, M.; Pesce-Rollins, M.; Petrucci, P.-O.; Pilia, M.; Possenti, A.; Poutanen, J.; Ramsey, B.; Rankin, J.; Roberts, O.; Romani, R.; Sgrò, C.; Slane, P.; Soffitta, P.; Spandre, G.; Swartz, D.; Tamagawa, T.; Tavecchio, F.; Taverna, R.; Tawara, Y.; Tennant, A.; Thomas, N.; Trois, A.; Tsygankov, S.; Turolla, R.; Vink, J.; Weisskopf, M.; Wu, K.; Xie, F.; Zane, S.
https://urn.fi/URN:NBN:fi-fe2025082787779
Tiivistelmä
Context. NGC 1068 is the most observed radio-quiet active galactic nucleus (AGN) in polarimetry, yet its high-energy polarization has never been probed before due to a lack of dedicated polarimeters.
Aims. Using the first X-ray polarimeter sensitive enough to measure the polarization of AGNs, we want to probe the orientation and geometric arrangement of (sub)parsec-scale matter around the X-ray source.
Methods. We used the Imaging X-ray Polarimetry Explorer (IXPE) satellite to measure, for the first time, the 2–8 keV polarization of NGC 1068. We pointed IXPE at the target for a net exposure time of 1.15 Ms, in addition to using two Chandra snapshots of ∼10 ks each in order to account for the potential impact of several ultraluminous X-ray sources (ULXs) within IXPE’s field of view.
Results. We measured a 2–8 keV polarization degree of 12.4% ± 3.6% and an electric vector polarization angle of 101° ± 8° at a 68% confidence level. If we exclude the spectral region containing bright Fe K lines and other soft X-ray lines where depolarization occurs, the polarization fraction rises to 21.3% ± 6.7% in the 3.5–6.0 keV band, with a similar polarization angle. The observed polarization angle is found to be perpendicular to the parsec-scale radio jet. Using a combined Chandra and IXPE analysis plus multiwavelength constraints, we estimated that the circumnuclear “torus” may sustain a half-opening angle of 50–55° (from the vertical axis of the system).
Conclusions. Thanks to IXPE, we have measured the X-ray polarization of NGC 1068 and found comparable results, both in terms of the polarization angle orientation with respect to the radio jet and the torus half-opening angle, to the X-ray polarimetric measurement achieved for the other archetypal Compton-thick AGN: the Circinus galaxy. Probing the geometric arrangement of parsec-scale matter in extragalactic objects is now feasible thanks to X-ray polarimetry.
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