X-ray polarization measurement of the gold standard of radio-quiet active galactic nuclei: NGC 1068

Journal
Date Issued
2024
Author(s)
Marin, F.
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Marinucci, A.
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Laurenti, M.
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Kim, D. E.
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Barnouin, T.
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•
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BIANCHI, Simone
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Ravi, S.
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Marshall, H. L.
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Matt, G.
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Taverna, R.
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Tawara, Y.
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Tennant, A.
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Thomas, N.
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Tsygankov, S.
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Turolla, R.
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Vink, J.
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Weisskopf, M.
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Wu, K.
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Zane, S.
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Chen, C. -T.
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Gianolli, V. E.
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Ingram, A.
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Middei, R.
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Maksym, W. P.
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Panagiotou, C.
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Podgorny, J.
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Puccetti, S.
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Ratheesh, A.
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Agudo, I.
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•
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Baldini, L.
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Baumgartner, W.
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Bellazzini, R.
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Bongiorno, S.
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Bonino, R.
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Brez, A.
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•
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Castellano, S.
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Cavazzuti, E.
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Ciprini, S.
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•
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Di Gesu, L.
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Di Lalla, N.
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Donnarumma, I.
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Doroshenko, V.
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Dovčiak, M.
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Ehlert, S.
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Enoto, T.
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•
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Ferrazzoli, R.
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Garcia, J.
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Gunji, S.
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Heyl, J.
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Iwakiri, W.
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Jorstad, S.
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Kaaret, P.
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Karas, V.
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Kislat, F.
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Kitaguchi, T.
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Kolodziejczak, J.
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Krawczynski, H.
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Latronico, L.
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Liodakis, I.
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Madejski, G.
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Maldera, S.
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Manfreda, A.
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Marscher, A.
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Mitsuishi, I.
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Mizuno, T.
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Negro, M.
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Ng, S.
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O'Dell, S.
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Omodei, N.
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Oppedisano, C.
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Pavlov, G.
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Pesce-Rollins, M.
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Petrucci, P. -O.
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Poutanen, J.
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Ramsey, B.
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Rankin, J.
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Roberts, O.
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Romani, R.
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Sgrò, C.
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Slane, P.
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Spandre, G.
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Swartz, D.
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Tamagawa, T.
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DOI
Abstract
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.
Volume
689
Start page
A238
Uri
Url
Issn Identifier
0004-6361
Ads BibCode
2024A&A...689A.238M
Rights
open.access
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