Radio Halo and Relic Candidates from the Westerbork Northern Sky Survey

We have undertaken a systematic search for diffuse radio halos and relics inall of the Abell clusters that are visible in the Westerbork Northern SkySurvey (WENSS). In this survey we found 18 candidates, 11 of which are alreadyknown from the literature, and 7 for which we provide the first evidence ofdiffuse radio emission. All the clusters in this sample show other evidence fora recent or ongoing merger. We also investigate the correlation between clusterX-ray luminosity and radio power of halos. We develop a very simple model formerger shocks that reproduces the sense of this correlation, although it isprobably not as steep as the correlation in the data. We discuss theimplications of X-ray--radio correlations for future detections of radio halos.