Secular Decreases in the 927 MHz Emission from the Supernova Remnants Cas A and Tau A

Abstract

This paper presents 927 MHz flux densities for the SNRs Cassiopeia A and TaurusA relative to those for the radio galaxies Cygnus A and Virgo A and for the Orion Nebula. The measurements were made in October-December 1977 with the 10 m radiotelescope at the Staraya Pustyn' (NIRFI) RadioastronomicaI Observatory. Comparison between these data and the absolute flux density measurements of Razin and Fedorov (1963) yields an annual decrease in flux density of 0·95%±0·04% for CasA and 0·18%±0·01% for TauA (14·2%±0·6% and 2·7%± 0·1% respectively over the past 15 years).