The physical parameters of several extragalactic radio sources displaying rapid variability

We present the results of a study of the sources PKS 0405-385, B0917+624, PKS 1257-326, and J1819+3845, which display variability on time scales from 1–7 h (at 5 GHz). Estimates of the physical parameters (magnetic-field intensity, density of relativistic particles, energies of the magnetic field and relativistic particles) are given for B0917+624 and J1819+3845. It is shown that these sources are not in a state of energy equipartition. A number of indirect arguments indicate that the shortest flares in sources with long-time-scale variability have the same parameters as flares in the studied sources.