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

F. Marin, A. Marinucci, M. Laurenti, D. E. Kim, T. Barnouin, A. Di Marco, F. Ursini, S. Bianchi, S. Ravi, H. L. Marshall, G. Matt, C. -T. Chen, V. E. Gianolli, A. Ingram, W. P. Maksym, C. Panagiotou, J. Podgorny, S. Puccetti, A. Ratheesh, F. Tombesi, I. Agudo, L. A. Antonelli, M. Bachetti, L. Baldini, W. Baumgartner, R. Bellazzini, S. Bongiorno, R. Bonino, A. Brez, N. Bucciantini, F. Capitanio, S. Castellano, E. Cavazzuti, S. Ciprini, E. Costa, A. De Rosa, E. Del Monte, L. Di Gesu, N. Di Lalla, I. Donnarumma, V. Doroshenko, M. Dovciak, S. Ehlert, T. Enoto, Y. Evangelista, S. Fabiani, R. Ferrazzoli, J. Garcia, S. Gunji, J. Heyl, W. Iwakiri, S. Jorstad, P. Kaaret, V. Karas, F. Kislat, T. Kitaguchi, J. Kolodziejczak, H. Krawczynski, F. La Monaca, L. Latronico, I. Liodakis, G. Madejski, S. Maldera, A. Manfreda, A. Marscher, F. Massaro, I. Mitsuishi, T. Mizuno, F. Muleri, M. Negro, S. Ng, S. O'Dell, N. Omodei, C. Oppedisano, A. Papitto, G. Pavlov, M. Perri, M. Pesce-Rollins, P. -O. Petrucci, M. Pilia, A. Possenti, J. Poutanen, B. Ramsey, J. Rankin, O. Roberts, R. Romani, C. Sgro, P. Slane, P. Soffitta, G. Spandre, D. Swartz, T. Tamagawa, F. Tavecchio, R. Taverna, Y. Tawara, A. Tennant, N. Thomas, A. Trois, S. Tsygankov, R. Turolla, J. Vink, M. Weisskopf, K. Wu, F. Xie, S. Zane

Published 2024-03-04, updated 2024-05-13Version 2

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 for a net exposure time of 1.15 Ms on the target, in addition to two ~ 10 ks each Chandra snapshots in order to account for the potential impact of several ultraluminous X-ray source (ULXs) within IXPE's field-of-view. We measured a 2 - 8 keV polarization degree of 12.4% +/- 3.6% and an electric vector polarization angle of 101{\deg} +/- 8{\deg} at 68% confidence level. If we exclude the spectral region containing the bright Fe K lines and other soft X-ray lines where depolarization occurs, the polarization fraction rises up 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 multi-wavelength constraints, we estimated that the circumnuclear "torus" may sustain a half-opening angle of 50{\deg} - 55{\deg} (from the vertical axis of the system). Thanks to IXPE, we have measured the X-ray polarization of NGC 1068 and found comparable results, both in terms of polarization angle orientation with respect to the radio-jet and 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 object is now feasible thanks to X-ray polarimetry.