Restarting radio activity in a hard X-ray selected sample
Radio activity is episodic in nature and radio galaxies witness such activity. However, the duration and the duty cycle of the jet activity is not known, notwithstanding its importance in the context of radio galaxy evolution and feedback to the environment. Due to their large scale and old age, Giant Radio Galaxies (GRG) are ideal targets to study the duty cycle of radio activity. However, GRG usually constitute only a small fraction of sources in radio surveys and a systematic study of the occurrence of restarting activity is still missing. Cross-correlating the INTEGRAL+Swift AGN population with radio catalogues (NVSS, FIRST, SUMSS), we found that 22% of the sources are GRG (a factor four higher than those selected from radio catalogues). Remarkably, all of the sources in the sample show signs of restarting radio activity. The X-ray properties are consistent with this scenario, the nuclei being in a high-accretion, high-luminosity state. I will discuss in details the multi-frequency evidence of restarting activity in this sample.