The variability of 3C 390.3

Continuum observations at X-ray, optical and radio frequencies of 3C 390.3 over a period of 10 yr, and also optical and X-ray spectra, are presented. The structures of the light curves are compared and variations in the optical line-strengths and profiles are used to examine the physical conditions and geometry of the nuclear regions. Estimates of the extinction of the narrow-line region are made. The ratios of Lα/Hα and Hα/Hβ are not consistent with simple reddening, suggesting that self-absorption processes are important. Variations of the [Fe X] emission line imply that it originates in regions of relatively high density for both collisional or photo-ionization models. Near to a time of minimum optical continuum, the hydrogen column density was found to be high, consistent with absorption of the continuum source by gas clouds, whose motion may also be responsible for the observed variations of the Balmer line profiles. (author)