Abstract
Context.Variations in the mass accretion rate appear to be responsible for the rapid transitions in spectral type that are observed in increasingly more active galactic nuclei (AGNs). These objects are now labeled “changing-look” AGNs and are key objects for understanding the physics of accretion onto supermassive black holes.Aims.We aim to complement the analysis and interpretation of changing-look AGNs by modeling the polarization variations that can be observed, in particular, polarized-light echoes.Methods.We built a complex and representative model of an AGN and its host galaxy and ran radiative transfer simulations to obtain realistic time-dependent polarization signatures of changing-look objects. Based on actual data, we allowed the system to become several times fainter or brighter within a few years, assuming a rapid change in accretion rate.Results.We obtain time-dependent polarization signatures of distant high-luminosity (quasars) and nearby low-luminosity (Seyferts) changing-look AGNs for a representative set of inclinations. We predict the evolution of the continuum polarization for future polarimetric campaigns with the goal to better understand the physics at work in these objects. We also investigate highly inclined AGNs that experience strong accretion rate variations without appearing to change state. We apply our modeling to Mrk 1018, the best-documented case of a changing-look AGN, and predict a variation in its polarization after the recent dimming of its continuum.Conclusions.We demonstrate that polarization monitoring campaigns that cover the transitions that are observed in changing-look AGNs might bring crucial information on the geometry and composition of all the reprocessing regions within the nucleus. In particular, specific features in the time variation of the polarization position angle can provide a new and efficient method for determining AGN inclinations.
Highlights
The optical spectrum of type 1 active galactic nuclei (AGNs) is characterized by broad and narrow emission lines, while the spectrum of type 2 AGNs only show narrow emission lines
We have undertaken a series of single-wavelength simulations to predict the polarization time variations of Changinglook AGNs (CLAGNs)
An orthogonal flip of the polarization position angle in type 1 CLAGNs provides a new method for estimating the inclination of the nucleus, independently of the associated spectroscopic signatures
Summary
The optical spectrum of type 1 active galactic nuclei (AGNs) is characterized by broad and narrow emission lines, while the spectrum of type 2 AGNs only show narrow emission lines. CLAGNs with appearing or disappearing broad emission lines (BELs) were first discovered among Seyfert galaxies, that is, nearby and low-luminosity AGNs (e.g., Khachikian & Weedman 1971; Cohen et al 1986; Goodrich 1989). Appeareance and disappeareance of BELs was discovered in highluminosity AGNs (quasars; LaMassa et al 2015; Runnoe et al 2016; Ruan et al 2016; MacLeod et al 2016). These spectral changes are accompanied by a dimming or a brightening of the continuum; the dimming corresponds to changes from type 1 to type 1.9/2, and the brighten to changes from type 1.9/2 to type 1. New CLAGNs are regularly identified (e.g., Gezari et al 2017; Assef et al 2018; Stern et al 2018; Wang et al 2018; Yang et al 2018; MacLeod et al 2019)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
