Timescales of Long-Term Optical Base-Level Fluctuations in Three Classes of AGN

The long-term optical light curves of many active galactic nuclei (AGN) disply smooth, cyclical changes in level on timescales of years. Earlier work by Smith et al. (1993) estimated the timescales of this previously undiscussed phenomenon for a sample of 60 classical radio-loud quasars. The present study extends the analysis to three additional groups of AGN: the BL Lacertids, the compact galaxies, and the radio-quiet quasars. The average timescale of the BL Lacertids is approximately equal to that of the classical quasars, lending credence to unified models of these objects. The long-term fluctuations of the compact galaxies and the radio-quiet quasars are slower. Our analysis tends to support the division of the BL Lacertids into two populations.

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