Secular Decrease and Random Variations of the Flux Density of Cas a at 927, 290, 151.5, and 38 MHZ from Long-Term Measurements

Long-term measurements of the radio flux density of Cassiopeia A relative to Cygnus A have been carried out at 927, 290, 151.5, and 38 MHz. The mean secular decreases in the radio flux of Cas A are d927 = -(0.73±0.05)% year-1 (for the period 1977.8-1996.8), d290 = -(0.66 ± 0.07)% year-1 (1978.8-1996.85), and d151.5 = -(1.11 ± 0.22)% year-1 (1980.9-1994.8). Using also the results of other studies, d38 = -(.66 ± 0.17)% year-1 (1956-1995.6) and d151.5 = -(.86 ± 0.09)% year-1 (1966.5-1994.8). The temporal nonuniformity of the Cas A flux density decrease is most likely due to random changes in the integrated radio emission of the approximately 300 compact features observed in this source.