A discovery of young radio sources in the cores of giant radio galaxies
  selected at hard X-rays
  Giant Radio Galaxies (GRG) are the largest single entities in the Universe,
having a projected linear size exceeding 0.7 Mpc, which implies that they are
also quite old objects. They are not common, representing a fraction of only
about 6% in samples of bright radio galaxies. While a census of about 300 of
these objects has been built in the past years, still no light has been shed on
the conditions necessary to allow such an exceptional growth, whether of
environmental nature or linked to the inner accretion properties. Recent
studies found that samples of radio galaxies selected from hard X-ray AGN
catalogs selected from INTEGRAL/IBIS and Swift/BAT (thus at energies >20 keV)
present a fraction of GRG four times larger than what found in radio-selected
samples. We present radio observations of 15 nuclei of hard X-ray selected GRG,
finding for the first time a large fraction (61%) of young radio sources at the
center of Mpc-scale structures. Being at the center of GRG, these young nuclei
may be undergoing a restarting activity episode, suggesting a link between the
detected hard X-ray emission - due to the ongoing accretion - and the
reactivation of the jets.
