Small Diameter Components in the Crab Nebula at 1,422 Mc/s

Abstract

PREVIOUS radio surveys of the Crab nebula at frequencies greater than 80 Mc/s show a generally smooth and slightly asymmetrical distribution of radio brightness with an angular extent of about 5 min of arc. The spectral index of this radiation is quite uniform over the source (approximately − 0.25 to −0.35) and can be explained as synchrotron emission. Recently, considerable interest has been aroused by the detection at Cambridge^1,2 of a small diameter source which comprised 30–50 per cent of the radiation at 26.5 Mc/s. This source was found to have an extraordinarily high spectral index (− 1.2), so that at 408 Mc/s it contributes only about 2.5 per cent of the total flux. Subsequently, observers at Parkes³ reported the results of a lunar occultation at 404 and 1,420 Mc/s. In addition to the large scale structure, smaller components of size less than 1 min of arc were also detected at both frequencies. These were found to correspond to regions of intense optical emission, and are labelled A, B and C in Fig. 1.