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8.4-GHZ radio imaging study of an optically selected sample of early typeSeyfert galaxies; comparison of images taken at two epochs reveals possiblevariation in the nuclear radio flux density in five of them over a seven yearperiod. It is shown that there is a possible correlation between the presenceof nuclear radio variability and the absence of hundred parsec-scale radioemission, analogous with radio-loud AGN. Our results suggest that all Seyfertsmay exhibit variation in their nuclear radio flux density at 8.4 GHz, but thatvariability is more easily recognized in compact sources in which emission fromthe variable nucleus is not diluted by unresolved, constant flux density radiojet emission within the central 50 pc. Taken in combination with other Seyfertproperties, these results suggest a paradigm of intermittent periods ofquiescence and nuclear outburst across the Seyfert population and demonstratethe importance of investigating the temporal domain at radio wavelengths, whichremains completely unexplored for faint radio-quiet AGN. Discovery ofintermittent activity and radio flares has important implications for the AGNduty cycles and the origin of Ultra-High Energy Cosmic Rays. New radiofacilities, such as the EVLA/VLBA, eMERLIN, LOFAR and eVLBI on the EVN, willrevolutionise the study of radio-quiet AGN; in particular, the combination ofincreased sensitivity and sampling rate with high-angular resolution andautomatic data reduction will open up the transient radio sky and bring majorfuture breakthroughs.

Radio-Quiet AGN and the Transient Radio Sky