Polarization constraints on the X-ray corona in Seyfert Galaxies: MCG-05-23-16

TL;DR

This study presents the first polarized X-ray observation of a radio-quiet AGN, MCG-05-23-16, constraining the geometry of its corona through polarization measurements and spectral analysis.

Contribution

It provides the first polarization measurement of a Seyfert galaxy's corona, constraining its geometry using IXPE, XMM-Newton, and NuSTAR data combined with Monte Carlo simulations.

Findings

Polarization degree is less than 4.7% in 2-8 keV range.

Spectral analysis yields a photon index of 1.85 and cutoff at 120 keV.

Corona geometry is consistent with lamp-post or conical models, but not slab unless inclination is low.

Abstract

We report on the first observation of a radio-quiet Active Galactic Nucleus (AGN) using polarized X-rays: the Seyfert 1.9 galaxy MCG-05-23-16. This source was pointed with the Imaging X-ray Polarimetry Explorer (IXPE) starting on May 14, 2022 for a net observing time of 486 ks, simultaneously with XMM-Newton (58 ks) and NuSTAR (83 ks). A polarization degree smaller than $\Pi<4.7\%$ (at the 99% c.l.) is derived in the 2-8 keV energy range, where emission is dominated by the primary component ascribed to the hot corona. The broad-band spectrum, inferred from a simultaneous fit to the IXPE, NuSTAR, and XMM-Newton data, is well reproduced by a power law with photon index $\Gamma=1.85\pm0.01$ and a high-energy cutoff $E_{\rm C}=120\pm15$ keV. A comparison with Monte Carlo simulations shows that a lamp-post and a conical geometry of the corona are consistent with the observed upper limit, a slab geometry is allowed only if the inclination angle of the system is less than 50$^{\circ}$.