Optical Monitoring of Radio Sources -- II: The N-type and Seyfert Galaxies

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Abstract
We have extended our optical monitoring programme for quasars that was described in Paper I of this series to include 19 N-type and Seyfert galaxies. A summary of all previous work on such objects is given. Light curves for ten of these objects are presented. I Zw 0051 + 12, II Zw 2130+09 are new variables and the suggested variability of NGC 1275 and NGC 7469 is confirmed. We find that the patterns of variability are similar to those found among quasars. Some quasar-like galaxies are optically violently variable (OVV) and among both OVV and non-OVV objects many show ‘standstills’ lasting of the order of one year. The proportion of Seyfert and N-type galaxies that are OVV is higher than for quasars. The correlation between OVV activity and flatness of the radio spectrum or radio variability is maintained for objects that are also radio sources. The light curves of 3C371 and 3C390.3 are strangely similar. The brightness of some N-galaxies in the past provides a ‘continuity’ argument, showing that some quasars at least are cosmological.

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