Optical Variations in 3C 446

Abstract

Cannon and Penston¹ have reported observations of the rapid optical fluctuations of the quasi-stellar object 3C 446. These add further to the study of rapid variations discovered in this object by Sandage² and followed in 1966 by Kinman, Lamla and Wirtanen³. Variations of this kind lead to the conclusion that the region which gives rise to the fluctuation is very small, and in general it is found that for this region R ⩽ c τ, where τ is the period over which a flux change has occurred. A detailed discussion of this result has been given by Terrell⁴ and others. These limitations lead to very restrictive conditions on the possible models of quasi-stellar objects which arise largely from the high radiation density that must be present in the continuum source. The upper limits to the sizes which have been used range from light months to light days (∼10¹⁷ — 10¹⁵ cm) and the corresponding lower limits to the energy densities are then in the range 10–10⁵ erg/cm³ if the quasi-stellar objects are at cosmo-logical distances, and 10⁻³–10 ergs/cm³ if the objects lie at distances ∼ 10 megaparsec (Mpc). If the objects are at cosmological distances, then this radiation field is so intense that it would be self-destructive, whether it arises by the synchrotron process or from the inverse Compton process^5,8. The difficulties that are encountered in arriving at satisfactory models, if the quasi-stellar objects are at cosmological distances, have been considered by Hoyle, Burbidge and Sargent⁵. Attempts to evade or to minimize these difficulties if the objects are at cosmological distances have been made by Rees⁶, by Woltjer⁷, and by Hoyle and Burbidge⁸, and they require that the radiating blobs are moving at relativistic speeds and/or that there is a large degree of directivity in the streams of relativistic electrons. If the quasi-stellar objects are much closer, the radiation density is accordingly reduced and the problems are less severe.