Annu. Rev. Astron. Astrophys. 1981. 19: 373-410 Copyright © 1981 by Annual Reviews. All rights reserved

6.1 Stationary Sources

The sources 3C 84 and 4C 39.25 have very low limits to any possible relative motion of components. Observations of 4C 39.25 made since 1973 show a double source with a maximum rate of separation less than 6 microarcsec per year (0.2 c) (Kellermann & Shaffer 1977, D.B. Shaffer, personal communication).

3C 84 is of particular interest, since it consists of three main emission regions located in the nucleus of NGC 1275 (Pauliny-Toth et al. 1976b, Matveyenko et al. 1980), which show no relative motion with an upper limit of only 10,000 km s^-1 (Preuss et al. 1979). The individual components, however, expand with an average velocity of about 30,000 km s^-1. The rate of increase of component size as well as the increase in flux density suggest a prolonged acceleration or injection of relativistic particles which began some 20 years ago. In both 3C 84 and 4C 39.25 the characteristic age obtained by dividing the overall component separation by the maximum possible velocity is at least 300 years. Yet, in both sources, there are large flux density variations on a time scale of 1 to 10 years. Thus, in these sources at least, the relativistic particles appear to be injected or accelerated in fixed, spatially separated components. But, at least in case of 3C 84, the similar ages deduced from the component expansion and flux density increase and the overall linear structure suggest that the separate emission regions are not independent but are perhaps excited by a wave or shock that propagates from a single origin.