The optical and X-ray properties of a sample of Seyfert galaxies that have undergone significant spectral change

This paper presents the initial findings of a study of the optical spectra of two sets of data for about 50 Seyfert galaxies taken 20 years apart. We compared the spectra for the different epochs and identify some objects where significant spectral changes occurred. We describe the nature of the spectral changes and collate available information about the X-ray properties of these AGN. In particular, we probe whether the degree of spectral variability, which may range from relatively steady to “changing look” AGN, correlates with any X-ray features. We attempt to interpret our findings in terms of possible physical models of these AGN.