The Radio Source Cassiopeia A

Abstract

THE high-resolution observations of the radio source Cassiopeia A by Ryle, Elsmore and Neville¹ show for the first time details of the structure of the source that suggest an interpretation of a feature of the nebulosity connected with the source the significance of which was not clear. The nebulosity is essentially a circular shell with an outer radius of 2.0 min of arc, but it shows a flare in position angle 70° that extends to a distance of about 3.8 min of arc from the centre². The long streaks of nebulosity plotted by Ryle et al. at the east side of the source (α = 23h 21m 21s; δ = + 58° 33.5′ and α = 23h 21m 31s; δ = + 58° 33.1′) are the brightest features of the flare. They and the fainter details of the flare extend radially while the features of the shell show no strongly preferential direction.