The GMRT Radio Halo Survey and Low Frequency Follow--up

The GMRT Radio Halo Survey, carried out at 610 MHz to investigate the statistical properties of cluster radio halos in a complete cluster sample selected in the redshift interval z=0.2-0.4, has significantly improved our understanding of the origin of cluster radio halos and relics. Here we briefly summarize the most relevant results of our investigation. A low frequency follow-up is in progress with the GMRT at 325 MHz and 240 MHz on the diffuse sources and candidated found at 610 MHz. We briefly report some preliminary results on these low frequency observations. Cluster radio halos with different radio spectral properties have been unexpectedly found.