Changing-look Seyfert galaxies with optical linear polarization measurements

TL;DR

This paper advocates for new optical polarization measurements of changing-look Seyfert galaxies to better understand their flux variability and the physical processes in their cores, highlighting the need for updated observational campaigns.

Contribution

It emphasizes the importance of modern spectro-polarimetric data to distinguish between different models explaining changing-look AGNs and calls for renewed observational efforts.

Findings

Past polarization data is outdated, mostly from the 80s and 90s.

Polarization measurements can help identify physical mechanisms in CLAGNs.

New campaigns are essential for advancing understanding of these objects.

Abstract

In this lecture note, we make the case for new (spectro)polarimetric measurements of "changing-look" AGNs (CLAGNs), a subclass of the AGN family tree that shows long-term (months to years) large flux variability associated with the appearance or disappearance of optical broad emission lines. We discuss how polarization measurements could help to distinguish which of the several scenarios proposed to explain such variations is/are the most likely. We collected past polarization measurements of nearby, Seyfert-like CLAGNs and take stock that almost all polarimetric information we have on those fascinating objects dates from the 80's and 90's. We thus explain how polarization could help us understand the physical processes happening in the first parsecs of CLAGNs and why new polarization monitoring campaigns are strongly needed.