Optically Violent Variables (OVVs)

In general, AGNs show continuum variability at all wavelengths at which they have been observed, from X-rays to radio wavelengths. A small subset of AGNs show short time-scale variations that are abnormally large, e.g. Deltam gtapprox 0.1 mag in the visible wavelengths on time scales as short as a day. In addition to their large variations in flux, they also tend to have high polarization (up to a few percent, as opposed to less than 1% for most AGNs) which also varies, in both magnitude and position angle, and these sources are always radio loud. These AGNs are known as ``optically violent variables'', or OVVs.

It is thought that both OVVs and BL Lacs are those AGNs which have a strong relativistically beamed component close to the line of sight. Collectively, OVVs and BL Lacs are sometimes referred to as ``blazars''. All known blazars are radio sources.

Adapted from B.M. Peterson An Introduction to Active Galactic Nuclei, Cambridge University Press, (1997)