Continuum variability in quasars and Seyfert galaxies

Abstract

Multiwavelength observations of AGN give several pieces of information which help advance our understanding of the physics of the core regions. Very good correlations at zero lag are found between the UV and visible domains, suggesting that the variability cannot be due to variations in thin accretion discs. A possible significant correlation is found between the UV and the radio emission of 3C 273, which might be due to links between accretion and non thermal activity. Although no correlation between the X-ray flux and other components can be found, analysis including spectral information suggests that the X-ray emission may be due to Comptonised EUV flux, at least in the galaxy NGC 5548.