Active galaxy unification in the era of X-ray polarimetry

TL;DR

This paper predicts that X-ray polarization signatures from AGN winds, influenced by flow geometry and resonance scattering, can distinguish between different AGN types and test wind models with future polarimetry missions.

Contribution

It introduces a model for X-ray polarization in AGN winds, linking polarization signatures to wind geometry and dynamics, and predicts detectable polarization levels for future missions.

Findings

X-ray polarization depends on wind hydrodynamics and resonance line scattering.

Predicted polarization signatures are 5-25% for type-2 AGNs in 0.1-10 keV range.

Future X-ray polarimetry missions can test AGN wind models.

Abstract

Active Galactic Nuclei (AGN), Seyfert galaxies and quasars, are powered by luminous accretion and often accompanied by winds which are powerful enough to affect the AGN mass budget, and whose observational appearance bears an imprint of processes which are happening within the central parsec around the black hole (BH). One example of such a wind is the partially ionized gas responsible for X-ray and UV absorption ('warm absorbers'). Here we show that such gas will have a distinct signature when viewed in polarized X-rays. Observations of such polarization can test models for the geometry of the flow, and the gas responsible for launching and collimating it. We present calculations which show that the polarization depends on the hydrodynamics of the flow, the quantum mechanics of resonance line scattering and the transfer of polarized X-ray light in the highly ionized moving gas. The results emphasize the three dimensional nature of the wind for modeling spectra. We show that the polarization in the 0.1-10 keV energy range is dominated by the effects of resonance lines. We predict a $5-25%$ X-ray polarization signature of type-2 objects in this energy range. These results are general to flows which originate from a cold torus-like structure, located $\sim 1$pc from the BH, which wraps the BH and is ultimately responsible for the apparent dichotomy between type 1 and type 2 AGNs. Such signals will be detectable by future dedicated X-ray polarimetry space missions, such as the NASA Gravity and Extreme Magnetism SMEX, GEMS.