Extragalactic radio sources with steep low frequency spectra

A asmple of radio sources at high galactic latitudes with spectral indices |$\alpha ^{178}_{38}\gt 1.2$| has been selected; 38 per cent are found to be associated with Abell&s rich clusters of galaxies. The data support a direct relation between the steep radio spectra and X-ray emission from the clusters. This result is most easily explained by ascribing a thermal origin to the X-ray emission.