X-ray polarization observations of NGC 2110 with IXPE

¹ Department of Physics and Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634, USA
² Dipartimento di Fisica e Astronomia (DIFA), Università di Bologna, via Gobetti 93/2, I-40129 Bologna, Italy
³ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti, 93/3, 40129 Bologna, Italy
⁴ Department of Astronomy, University of Virginia, P.O. Box 400325 Charlottesville, VA 22904, USA
⁵ NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁶ European Southern Observatory, Alonso de Córdova 3107, Casilla 19, Santiago 19001, Chile

^⋆ Corresponding author: ipal@clemson.edu

Received: 31 December 2024
Accepted: 29 March 2025

Abstract

Context. X-ray polarimetric observations from the Imaging X-ray Polarimeter Explorer (IXPE) is an excellent tool for probing the geometry and dynamics of X-ray emitting corona in active galactic nuclei (AGNs).

Aims. This work aims to investigate the geometry of the X-ray corona in the Seyfert 2 AGN, NGC 2110, using its first polarimetric observation with IXPE, conducted over a net exposure of 554 ks beginning on October 16, 2024.

Methods. We performed a model-independent analysis of the 2–8 keV IXPE polarimetric observation to estimate the polarization properties of NGC 2110. Furthermore, we performed spectral and spectro-polarimetric analyses combining IXPE data with archival observations from NuSTAR, XMM-Newton, and Swift-XRT to derive detailed spectral and polarization properties.

Results. From the spectro-polarimetric analyses, an upper limit on the polarization degree (Π_X) of 7.6% (at the 99% confidence) was estimated in the 2–8 keV band. The spectro-polarimetric analysis in the 5.66–8 keV band yielded a looser upper limit of ≲27% at the 99% confidence. This result aligns closely with the findings from the model-independent analysis.

Conclusions. Comparing the measured polarization properties, coronal parameters, and inclination angle of NGC 2110 with the Monte Carlo radiative transfer (MONK) simulations suggest that the current polarization measurements lack the sensitivity to place definitive constraints on the coronal geometry. The upper limits on Π_X, as derived from our analysis at the 99% confidence level, indicate that polarization remains undetected at a statistically significant level. Consequently, we are unable to determine whether the corona is elongated along the disk or more compact and spherical. Future observations with improved sensitivity will be crucial to breaking these degeneracies and providing deeper insight into the coronal structure of NGC 2110.