A High-Resolution Map of Cassiopeia A at 2.7 GHz

Abstract

Observations of Cas A (3C 461) have been made using the Cambridge One-mile telescope at a frequency of 2695 MHz with a beamwidth of $$12^{\prime\prime} \times 14^{\prime\prime}$$ arc. The high resolution has revealed complex structure in the source and some of the spurs observed previously at a lower resolution have been found to be separated compact components of high emissivity. By comparing the new observations with earlier ones made at 1407 MHz variations of structure with frequency across the source have been found, with spectral indices higher on average on the west half of the source than on the east. Comparisons with optical photographs show a remarkable correlation between the gaps in the radio shell and some of the high velocity optical filaments. Estimates of some physical parameters of the main source and of the compact components are derived in the last part of the paper.