Abstract :
[en] Changing-look AGN are a extraordinary type of AGN which represents a violation of the AGN unified model. Studying this class of objects in polarized light helps us to shade light on the sub-parsec AGN structure and find out which additional ingredients are needed so that the unified model can describe the complex AGN taxonomy.
We carried out a detailed analysis of multi-epoch observations of the Seyfert galaxy ESO 362-G18 in X- ray, UV and optical ranges. In total, 45 X-ray observations and 4 optical data sets, 2 of them in polarized light, ranging from January 2003 till March 2016.
The four optical analyzed spectra reveal ESO362-G18 as a changing-look Seyfert galaxy, since two spectra are of type 1.5 and the remaining two show ESO362-G18 as a type 1.9 AGN. We have polarized measurements of one of the type 1.5 data sets and also one of the type 1.9, allowing us to compare the polarization properties in both states of a changing-look Seyfert galaxy by first time.
From the X-ray data set, we found ESO362-G18 to exhibit relativistic reflection, including a detected soft time lag between continuum and reflection components, whose results support the compact nature of the X-ray emitting regions. We proved a very rapidly spinning Kerr back hole and a very high inclination of ~53o(in two ways, dependent and independent model; see Agís-González et al 2014). Thanks to this derived model, we have also detected two absorption events driven by clouds situated at torus scales.
The relatively high inclination we derived is consistent with the idea that our LOS is grazing the obscuring torus (which has a typical half-opening angle of the order of 45o). If the torus is not homogeneous but clumpy, such high inclination may intercept from time to time some of the clumps of the obscuring torus, explaining the detected X-ray absorption events and possibly why ESO362-G18 exhibits changes of look from type 1 to type 2 in its optical spectra. Moreover, the X-ray luminosity keeps roughly constant along the available observation, which discard a change in the accretion rate. Therefore, we will discuss the polarized properties of this intriguing changing-look Seyfert galaxy whose change of look is probably due to absorption in our LOS. At the same time, we will also expose optical polarimetry as a diagnostic tool to disentangle the cause of changes of look.
