2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/10667The continuum variability of optically selected Active Galactic Nuclei (AGN) is found to be consistent with that expected from a simple Poissonian process, in which the total luminosity of an object is produced by the multiple superposition of identical pulses. The energies, time-scales and rates of the pulses are found to be in the range of those expected from supernovae which generate fast evolving remnants in a nuclear starburst.However, radio-loud AGN don't follow the predictions of that simple scenario.6 pages, 2 Postscript figures, uses rmaaconf.sty, invited talk in 'Starburst Activity in Galaxies', to be published in Rev. Mex. Astr., also available in http://www.ast.cam.ac.uk/~itziarAstrophysicstext