The ultraviolet variability of Seyfert 1 galaxies.

Abstract

Multiple IUE spectra of nine Seyfert 1 galaxies, obtained over four years, were examined. Spectra of Mrk 509, ESO 141-G55, Fairall 9, III Zwicky 2, Mrk 279, NGC 3783, NGC 4593, NGC 7213, and NGC 7469 were examined for evidence of variability in both continuum and emission-line fluxes. All except NGC 7213 and III Zw 2 show 20 percent-80 percent continuum flux variations between 1200 and 1900 angstroms. Variations of 8 percent-30 percent were found in the emission-line fluxes of ESO 141-G55, III Zw 2, NGC 3783, NGC 4593, and NGC 7213. Both the amplitude and the time scale of the continuum variations are uncorrelated with either the UV or X-ray luminosity of the source; the variability may be caused, at least in part, by obscuring clouds along the line of sight from the continuum source.