The variability of the optical counterparts of four extragalactic radio sources.

The optical variability of four extragalactic radio sources has been studied using the archival plates at the Harvard College Observatory. Three of these sources, PKS 1123 + 264, B2 1132 + 303, and 4C 18.36, were conclusively found to exhibit significant optical variability. No conclusive evidence was found for optical variability for B2 1128 + 315 with a range of less than 0.3 magnitude,, based on a limited number of plates.