XPE and VLT /FORS2 polarimetry challenge the Seyfert-1.9 classification of MCG-05-23-16
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| Format: | Preprint |
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2026
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| _version_ | 1866908775943766016 |
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| author | Marin, Frédéric Tagliacozzo, Daniele Ursini, Francesco Hutsemékers, Damien Kokubo, Mitsuru Barnouin, Thibault Gnarini, Andrea Lai, Alessandro Leonardo Svoboda, Jirí Bianchi, Stefano Gianolli, Vittoria Elvezia Gau, Ephraim Hu, Kun Krawczynski, Henric Maksym, W. Peter Marinucci, Andrea Marshall, Herman Matt, Giorgio Middei, Riccardo Petrucci, Pierre-Olivier Puccetti, Simonetta Rodriguez, Nicole Serafinelli, Roberto Tombesi, Francesco |
| author_facet | Marin, Frédéric Tagliacozzo, Daniele Ursini, Francesco Hutsemékers, Damien Kokubo, Mitsuru Barnouin, Thibault Gnarini, Andrea Lai, Alessandro Leonardo Svoboda, Jirí Bianchi, Stefano Gianolli, Vittoria Elvezia Gau, Ephraim Hu, Kun Krawczynski, Henric Maksym, W. Peter Marinucci, Andrea Marshall, Herman Matt, Giorgio Middei, Riccardo Petrucci, Pierre-Olivier Puccetti, Simonetta Rodriguez, Nicole Serafinelli, Roberto Tombesi, Francesco |
| contents | We report the third observation of the Seyfert-1.9 active galactic nucleus (AGN) MCG-05-23-16 with the Imaging X-ray Polarimetry Explorer (\textit{IXPE}), together with optical spectro-polarimetry obtained at the Very Large Telescope (VLT), and combined with archival near-ultraviolet, optical and near-infrared polarimetric data. No X-ray polarization was detected in the 2-8 keV band, with a 99\% confidence upper limit of $\leq$2.9\%, further reduced to $\leq$2.5\% when combined with the two past IXPE observations of the same target. Monte Carlo simulations suggest that equatorial coronal models are disfavored if the AGN is indeed a type-1.9/2 AGN, but coronae coplanar to the accretion disk remain consistent if the source is less inclined than previously assumed. \textit{VLT}/FORS2 data reveal a typical type-2 spectrum in total flux, a broad H$α$ line in polarized flux, and strongly wavelength dependent polarization degree and angle, rotating by nearly 70$^\circ$ across the optical band. Comparison with historical measurements confirms long-term stability of the polarization spectrum and a $\sim$90$^\circ$ rotation in the near-ultraviolet. Interpreting the multi-wavelength polarization relative to the AGN ionization axis indicates that the main obscurer is not a compact circumnuclear torus, but a distant kpc-scale dust lane crossing the galaxy. This result implies that MCG-05-23-16 is in fact a type-1 AGN seen through foreground dust. The low X-ray column density becomes consistent with the absence of polarization, provided that the nuclear inclination is low. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2601_13701 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | XPE and VLT /FORS2 polarimetry challenge the Seyfert-1.9 classification of MCG-05-23-16 Marin, Frédéric Tagliacozzo, Daniele Ursini, Francesco Hutsemékers, Damien Kokubo, Mitsuru Barnouin, Thibault Gnarini, Andrea Lai, Alessandro Leonardo Svoboda, Jirí Bianchi, Stefano Gianolli, Vittoria Elvezia Gau, Ephraim Hu, Kun Krawczynski, Henric Maksym, W. Peter Marinucci, Andrea Marshall, Herman Matt, Giorgio Middei, Riccardo Petrucci, Pierre-Olivier Puccetti, Simonetta Rodriguez, Nicole Serafinelli, Roberto Tombesi, Francesco High Energy Astrophysical Phenomena Astrophysics of Galaxies 85-06 J.2.3; J.2.9 We report the third observation of the Seyfert-1.9 active galactic nucleus (AGN) MCG-05-23-16 with the Imaging X-ray Polarimetry Explorer (\textit{IXPE}), together with optical spectro-polarimetry obtained at the Very Large Telescope (VLT), and combined with archival near-ultraviolet, optical and near-infrared polarimetric data. No X-ray polarization was detected in the 2-8 keV band, with a 99\% confidence upper limit of $\leq$2.9\%, further reduced to $\leq$2.5\% when combined with the two past IXPE observations of the same target. Monte Carlo simulations suggest that equatorial coronal models are disfavored if the AGN is indeed a type-1.9/2 AGN, but coronae coplanar to the accretion disk remain consistent if the source is less inclined than previously assumed. \textit{VLT}/FORS2 data reveal a typical type-2 spectrum in total flux, a broad H$α$ line in polarized flux, and strongly wavelength dependent polarization degree and angle, rotating by nearly 70$^\circ$ across the optical band. Comparison with historical measurements confirms long-term stability of the polarization spectrum and a $\sim$90$^\circ$ rotation in the near-ultraviolet. Interpreting the multi-wavelength polarization relative to the AGN ionization axis indicates that the main obscurer is not a compact circumnuclear torus, but a distant kpc-scale dust lane crossing the galaxy. This result implies that MCG-05-23-16 is in fact a type-1 AGN seen through foreground dust. The low X-ray column density becomes consistent with the absence of polarization, provided that the nuclear inclination is low. |
| title | XPE and VLT /FORS2 polarimetry challenge the Seyfert-1.9 classification of MCG-05-23-16 |
| topic | High Energy Astrophysical Phenomena Astrophysics of Galaxies 85-06 J.2.3; J.2.9 |
| url | https://arxiv.org/abs/2601.13701 |