Yearly Variations of 3C 120

Abstract

THE photographic light curve¹ of the Seyfert galaxy 3C 120 shows a large-amplitude (∼1.2 magnitudes) long-term decline in brightness over five consecutive seasons from 1934/35 to 1939/40. Short-term fluctuations of smaller amplitude (∼0.3 to 0.6 magnitudes) with decline times of about 200 days are apparently superimposed on this decline¹, and the question immediately arises whether these fluctuations are intrinsic to the source or are due to some yearly observational selection effect. Kinman² has pointed out the existence of an hour-angle effect for 3C 345 and inspection of the hour angles of the 3C 120 plates reveals that the hour angles are selectively larger at the beginning and end of the season than in the middle. In this report we conclude that the yearly fluctuations in 3C 120 are almost certainly intrinsic to the source.