Modeling the reverberation of optical polarization in AGN

TL;DR

This paper models the reverberation of optical polarization in AGN using a Monte Carlo radiative transfer approach, revealing how geometry and inclination affect observable time lags and polarization, aiding in understanding AGN structure.

Contribution

It introduces a time-dependent Monte Carlo model for AGN reverberation, highlighting the impact of geometry and inclination on polarization and time lag responses.

Findings

Time lags and polarization depend strongly on AGN geometry.

Edge-on and face-on views show distinct flux and lag signatures.

Model results can help determine AGN orientation in Seyfert galaxies.

Abstract

According to the standard paradigm, the strong and compact luminosity of active galactic nuclei (AGN) is due to multi-temperature black body emission originating from an accretion disk formed around a supermassive black hole. This central engine is thought to be surrounded by a dusty region along the equatorial plane and by ionized winds along the poles. The innermost regions cannot yet be resolved neither in the optical nor in the infrared and it is fair to say that we still lack a satisfactory understanding of the physical processes, geometry and composition of the central (sub-parsec) components of AGN. Like spectral or polarimetric observations, the reverberation data needs to be modeled in order to infer constraints on the AGN geometry (such as the inner radius or the half-opening angle of the dusty torus). In this research note, we present preliminary modeling results using a time-dependent Monte Carlo method to solve the radiative transfer in a simplified AGN set up. We investigate different model configurations using both polarization and time lags and find a high dependency on the geometry to the time-lag response. For all models there is a clear distinction between edge-on or face-on viewing angles for fluxes and time lags, the later showing a higher wavelength-dependence than the former. Time lags, polarization and fluxes point toward a clear dichotomy between the different inclinations of AGN, a method that could help us to determine the true orientation of the nucleus in Seyfert galaxies.