On the problem of explaining decimeter flux variations in 3C 454.3 and other extragalactic sources

Attempts to understand flux variations at 408 MHz of the QSO 3C 454.3 and other extragafactic radio sources are described. If 3C 454.3 is at a cosmological distance (luminosity distance 5000 Mpc), the variations have occurred on a time scale 1/50 of the light travel time across the source. For this source it is shown that models utilizing moving "searchlight images" or small spatially independent sources are implausible. Expanding source models probably can be made to account for the variations. However, if the source is at a cosmological distance, the expansion velocity must be 0.9998c and it is necessary to mock up an inhomogeneous model which gives the appearance of a source expanding nonrelativistically. There are also serious problems associated with understanding how such a highly energetic relativistic cloud is not slowed down by the matter giving rise to the optical emission-line spectrum of this QSO, thereby giving rise to large changes in the line spectrum. The simplest way of explaining the observations is to suppose that the source is at a distance 100 Mpc, since in this case a cloud expanding nonrelativistically is adequate. It is shown that these arguments can be applied to CTA 102 and other sources which vary on time scales of years in this frequency range. Subject headings: cosmology - quasi-stellar sources or objects - radio sources