Contribution of parsec-scale material onto the polarized X-ray spectrum of type-1 Seyfert galaxies

TL;DR

This study investigates how distant parsec-scale material influences the polarized X-ray spectrum of type-1 Seyfert galaxies, revealing that reprocessing affects polarization measurements by up to 1 percentage point, which is crucial for accurate modeling.

Contribution

It provides the first detailed Monte Carlo radiative transfer analysis of the impact of remote circumnuclear material on X-ray polarization in type-1 AGN.

Findings

Polarization depends strongly on initial disk-corona polarization.

Reprocessing can alter polarization degree by up to 1%.

Effects vary with photon polarization and energy, especially above 10 keV.

Abstract

Type-1 radio-quiet active galactic nuclei (AGN) are seen from the polar direction and offer a direct view of their central X-ray engine. If most of X-ray photons have traveled from the primary source to the observer with minimum light-matter interaction, a fraction of radiation is emitted at different directions and is reprocessed by the parsec-scale equatorial circumnuclear region or the polar outflows. It is still unclear how much the polarization expected from type-1 AGN is affected by radiation that have scattered on the distant AGN components. In this paper, we examine the contribution of remote material onto the polarized X-ray spectrum of type-1 Seyfert galaxies using radiative transfer Monte Carlo codes. We find that the observed X-ray polarization strongly depends on the initial polarization emerging from the disk-corona system. For unpolarized and parallelly polarized photons (parallel to the disk), the contribution is negligible below 3 keV and tends to increase the polarization degree by up to one percentage points at higher energies, smoothing out the energy-dependent variations of the polarization angle. For perpendicularly polarized corona photons, the addition of the circumnuclear scattered (parallel) component adds to the polarization above 10 keV, decreases polarization below 10 keV and shifts the expected 90 deg rotation of the polarization angle to lower energies. In conclusion, we found that simulations of Seyfert-1s that do not account for reprocessing on the parsec-scale equatorial and polar material are under- or over-estimating the X-ray polarization by 0.1 - 1 percentage points.