The relationship between the X-ray and optical variability can give us important clues about the interaction and relationship between physically separated part of the system. Our long term optical monitoring programme of a sample of AGN have revealed a correlation between the short timescale (~days) X-ray and optical variations in these galaxies, suggesting that the optical emission results from X-ray reprocessing by the accretion disc.

However, in addition, there are long-term (several years) variations in the optical light curve, which does not occur in the X-ray lightcurve. These long timescale variations may be accounted for by allowing the disc accretion rate or the geometry of the system to vary over timescales of months - years.

Quick links:

• Find out more about the variability of Markarian 79 in this MNRAS paper
  (Alternatively: arXiv:0812.0810)
• The results of 12 years of monitoring NGC4051 is published here, in MNRAS
  (Alternatively: arXiv:0912.0544)

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