We report 1405 MHz measurements of the flux density of the \approx 320 year old supernova remnant Cassiopeia A , relative to the flux density of Cygnus A , made between 1995 and 1999 .
When compared to measurements made between 1957 and 1976 , we find that the rate at which Cassiopeia A has been fading at this and nearby frequencies has changed from \approx 0.9 % yr ^ { -1 } in the 1960s to \approx 0.6 - 0.7 % yr ^ { -1 } now .
Furthermore , we have collected from the literature measurements of this fading rate at lower ( 38 – 300 MHz ) and higher ( 7.8 – 16.5 GHz ) frequencies .
We show that the fading rate has dropped by a factor of \approx 3 over the past 50 years at the lower frequencies , while remaining relatively constant at the higher frequencies , which is in agreement with the findings of others .
Our findings at 1405 MHz , in conjunction with a measurement of the fading rate at the nearby frequency of 927 MHz by Vinyajkin ( 1997 ) , show an intermediate behavior at intermediate frequencies .
We also find that Cassiopeia A , as of \approx 1990 , was fading at about the same rate , \approx 0.6 - 0.7 % yr ^ { -1 } , at all of these frequencies .
Future measurements are required to determine whether the fading rate will continue to decrease at the lower frequencies , or whether Cassiopeia A will now fade at a relatively constant rate at all of these frequencies .