Changing-look Narrow-Line Seyfert 1s?

TL;DR

This paper explores the phenomenon of changing-look AGNs, especially in Narrow-Line Seyfert 1s, discussing observational evidence, potential causes like TDEs, and implications for AGN unification models.

Contribution

It provides multi-wavelength monitoring of NGC 2617 and discusses the rarity and possible mechanisms of changing-look phenomena in NLS1s, highlighting the role of orientation and dust sublimation.

Findings

Few CL NLS1s observed, mostly in X-ray.

Changing-look events may be caused by TDEs or star encounters.

Orientation and dust sublimation influence NLS1 appearance.

Abstract

Two major challenges to unification schemes for active galactic nuclei (AGN) are the existence of Narrow-Line Seyfert 1s (NLS1s) and the existence of changing-look (CL) AGNs. AGNs can drastically change their spectral appearance in the optical (changing their Seyfert type) and/or in the X-ray region. We illustrate the CL phenomenon with our multi-wavelength monitoring of NGC 2617 and discuss its properties compared with NLS1s. There are few examples of CL NLS1s and the changes are mostly only in the X-ray region. It has been proposed that some of these could be cases of a tidal-disruption events (TDE) or supernova events. If BLRs have a flat geometry and NLS1s are seen face-on then we have to see CL cases only if the orientation of the BLR changes as a result of a TDE or a close encounter of a star without a TDE. If NLS1s include both high Eddington accretion rate and low-inclination AGNs then a significant fraction of NLS1s could be obscured and would not be identified as NLS1s. CL cases might happen more in such objects if dust sublimation occurs following a strong increase in the optical luminosity.