AGN variability: from Seyfert nuclei to QSOs
  The 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. 
Itziar Aretxaga (Royal Greenwich Observatory)