A second view on the X-ray polarization of NGC 4151 with IXPE

• Published in: Astronomy and astrophysics (Berlin) 2024-10, Vol.691
• Main Authors: Gianolli, V E, Bianchi, S., Kammoun, E., Gnarini, A., Marinucci, A., Ursini, F., Parra, M., Tortosa, A., De Rosa, A., Kim, D E, Marin, F., Matt, G., Serafinelli, R., Soffitta, P., Tagliacozzo, D., Di Gesu, L., Done, C., Marshall, H L, Middei, R., Mikusincova, R., Petrucci, P-O., Ravi, S., Svoboda, J., Tombesi, F.
• Format: Article
• Language: English
• Subjects: Sciences of the Universe
• ISSN: 0004-6361; 1432-0756
• DOI: 10.1051/0004-6361/202451645

We report on the second observing program of the active galactic nucleus NGC 4151 with simultaneous Imaging X-ray Polarimetry Explorer (IXPE; 750 ks), NuSTAR (∼60 ks), XMM-Newton (∼75 ks), and NICER (∼65 ks) pointings. NGC 4151 is the first Type-1 radio-quiet Seyfert galaxy with constrained polarization properties for the X-ray corona. Despite the lower flux state in which the source was re-observed and the resulting higher contribution of the constant reflection component in the IXPE energy band, our results are in agreement with the first detection. From polarimetric analysis, a polarization degree Π = 4.7 ± 1.3% and polarization angle Ψ = 77° ± 8° east of north (68% c.l.) were derived in the 2.0–8.0 keV energy range. Combining the two observations leads to polarization properties that are more constrained than those of the individual detections, showing Π = 4.5 ± 0.9% and Ψ = 81° ± 6° (with a detection significance of ∼4.6 σ ). The observed polarization angle aligns very well with the radio emission in this source, supporting, together with the significant polarization degree, a slab or wedge geometry for the X-ray corona. However, a switch in the polarization angle at low energies (37° ±7° in the 2–3.5 keV bin) suggests the presence of another component. When it is included in the spectro-polarimetric fit, a high polarization degree disfavors an interpretation in terms of a leakage through the absorbers, instead pointing to scattering from some kind of mirror.