The ultraviolet continuum of quasars -II. Continuum variability.

Abstract

We present data on the variability of the ultraviolet continuum for a large sample of quasars observed with IUE. No variability was found on time- scales of days, but is common on time-scales of weeks to months. There is no correlation between the two-folding time-scale and luminosity, although the sampling rate is poor. For most of the quasars the ultraviolet continuum level varied over a range < 1mag, and there is a trend for the amplitude of the variability to decrease with increasing luminosity. In contrast to Seyfert galaxies, we find little evidence for variability in the shape of the ultraviolet continuum for quasars. For Seyfert galaxies the va;ability of the shape of the ultraviolet continuum may be due to the interplay between several continuum components, whereas for quasars a single component may dominate.