A Radio Source with a Very Unusual Spectrum

Conway, Kellerman and Long¹ have recently determined the spectra of 160 radio sources in the wave-length range of 10 cm-26 m. Their results were obtained by combining measurements at nine wave-lengths made at the California Institute of Technology, Mullard and Nuffield Radio Observatories. At wave-lengths longer, than 20 cm they found that most of the spectra could be represented by power laws and that the median spectral slope was 0.7. Two notable exceptions are the sources CTA 21 and CTA 102 (ref. 2) which have curved spectra with maxima in the region of 30-50 cm. These two objects were originally found from observations at 30 cm whereas all the others were selected from the 3C (ref. 3) and the Mills, Slee and Hill (MSH) (ref. 4) catalogues. As these surveys were made at wave-lengths of 2 and 3.5 m respectively, selection from them would tend to discriminate against objects of the type of CTA 21 and CTA 102. Kellerman (private communication) has pointed out that it is important to know the relative population of such sources because of their possible influence on source counts at different wave-lengths.