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.
@article{arxiv.1810.08844,
title = {Changing-look Narrow-Line Seyfert 1s?},
author = {Victor L. Oknyansky and Konstantin L. Malanchev and C. Martin Gaskell},
journal= {arXiv preprint arXiv:1810.08844},
year = {2019}
}
Comments
6 pages, 1 figures, Revisiting narrow-line Seyfert 1 galaxies and their place in the Universe (NLS1-2018)