AN OBJECTIVE SURVEY OF Mpc-SCALE RADIO EMISSION IN 0.03 <z< 0.3 BRIGHT X-RAY CLUSTERS

Abstract

We have performed the the first census of Mpc-scale radio emission to include control fields and quantifiable upper limits for bright X-ray clusters in the range 0.03<z<0.3 . Through reprocessing radio images from the WENSS survey, we detect diffuse emission from approximately 30% of the sample. We find a correlation similar to the well-studied relationship between radio halo and X-ray luminosities of the host cluster, but also find that large scale radio galaxy detections follow a similar trend to that for radio halos. With this quantitative study, we thus confirm the upper envelope to the radio luminosities for X-ray selected clusters, and the higher detection rates for diffuse radio emission (including halos, relics and radio galaxies) at X-ray luminosities above approximately 10**45 erg/s. We can neither confirm nor refute the claims for a tight correlation between these radio halo and X-ray luminosities, i.e. whether the halo luminosity function of X-ray clusters is bimodal (having high/on and low/off states), or whether the radio luminosity can take on a wide range of values up to a maximum at each cluster X-ray luminosity. The resolution of this issue may provide a unique diagnostic for the timescales over which relativistic particles can be accelerated following cluster mergers. We discuss several important selection effects on radio vs. X-ray luminosity correlations, including surface brightness thresholds and non-X-ray-selected diffuse radio sources. We also report several new detections of diffuse emission, including a Mpc-scale relic in RXJ1053.7+5450, a possible halo/relic combination in Abell 2061, a serendipitous diffuse X-ray source associated with poor clusters in the Abell 781 field, and confirmation of very weak diffuse emission patches outside of Abell~2255.