Modeling the polarization of radio-quiet AGN from the optical to the X-ray band

TL;DR

This study models the spectropolarimetric signatures of radio-quiet AGN across optical, UV, and X-ray bands using Monte Carlo simulations, predicting polarization features for future X-ray polarimetry missions.

Contribution

It introduces a comprehensive radiative transfer model that links optical/UV and X-ray polarization signatures in AGN, incorporating complex geometries and reprocessing media.

Findings

Optical/UV polarization dichotomy extends into X-ray band.

Predicted polarization degrees and angles for future X-ray missions.

Model aligns optical/UV observations with X-ray polarization expectations.

Abstract

A thermal active galactic nucleus (AGN) consist of a powerful, broad-band continuum source that is surrounded by several reprocessing media with different geometries and compositions. Here we investigate the expected spectropolarimetric signatures in the optical/UV and X-ray wavebands as they arise from the complex radiative coupling between different, axis-symmetric AGN media. Using the latest version of the Monte-Carlo radiative transfer code STOKES, we obtain spectral fluxes, polarization percentages, and polarization position angles. In the optical/UV, we assume unpolarized photons coming from a compact source that are reprocessed by an optically-thick, dusty torus and by equatorial and polar electron-scattering regions. In the X-ray band, we additionally assume a lamp-post geometry with an X-ray source irradiating the accretion disk from above. We compare our results for the two wavebands and thereby provide predictions for future X-ray polarimetric missions. These predictions can be based on present-day optical/UV spectropolarimetric observations. In particular, we conclude that the observed polarization dichotomy in the optical/UV band should extend into the X-ray range.