The Expanding radio lobe of 3C 84 revealed by VSOP observations

The expansion and inner proper motions of a young radio lobe associated with the bright radio source 3C 84 in the Seyfert galaxy NGC 1275 have been detected by VSOP observations. These proper motions are consistent with the evolution scenario of classical double radio sources. The apparent expansion velocity is (0.50 +/- 0.09) c. The age of the radio lobe is estimated to be (45.7 +/- 8.9) yr in 2001, which is in agreement with the age previously estimated by Romney et al. (1982). The total flux density at 5 GHz increased at the end of the 1950's, marked several peaks in the middle of: the 1980's, and is presently in a decay phase. The decay of the total flux density can naturally be explained by an adiabatic cooling due to expansion of the radio lobe, and previously measured spectral indices Suggest that the emission comes from the surface of the radio lobe.