  We report on new VLA radio observations of the distant cluster RX
J1347.5-1145, which is the most luminous in X-rays. We aim at investigating the
possible presence of diffuse and extended radio emission in this very peculiar
system which shows both a massive cooling flow and merging signatures. New low
resolution (~18 arcsec) VLA radio observations of this cluster are combined
with higher resolution (~2 arcsec) data available in the VLA archive. We
discover the presence of a diffuse and extended (~500 kpc) radio source
centered on the cluster, unrelated to the radio emission of the central AGN.
The properties of the radio source, in particular a) its occurrence at the
center of a massive cooling flow cluster, b) its total size comparable to that
of the cooling region, c) its agreement with the observational trend between
radio luminosity and cooling flow power, indicate that RX J1347.5-1145 hosts a
radio mini-halo. We suggest that the radio emission of this mini-halo, which is
the most distant object of its class discovered up to now, is due to electron
re-acceleration triggered by the central cooling flow. However, we also note
that the morphology of the diffuse radio emission shows an elongation
coincident with the position of a hot subclump detected in X-rays, thus
suggesting that additional energy for the electron re-acceleration might be
provided by the submerger event.
