Kavli Affiliate: Herman Marshall
| Summary:
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 (textitIXPE), 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$2.5% when combined with the two past IXPE observations of the same target. Monte Carlo simulations suggest that equatorial coronal models are disfavored if the AGN is indeed a type-1.9/2 AGN, but coronae coplanar to the accretion disk remain consistent if the source is less inclined than previously assumed. textitVLT/FORS2 data reveal a typical type-2 spectrum in total flux, a broad H$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.
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