Flat-spectrum radio sources as likely counterparts of unidentified
  INTEGRAL sources (Research Note)
  Many sources in the fourth INTEGRAL/IBIS catalogue are still unidentified,
since they lack an optical counterpart. An important tool that can help in
identifying/classifying these sources is the cross-correlation with radio
catalogues, which are very sensitive and positionally accurate. Moreover, the
radio properties of a source, such as the spectrum or morphology, could provide
further insight into its nature. Flat-spectrum radio sources at high Galactic
latitudes are likely to be AGN, possibly associated to a blazar or to the
compact core of a radio galaxy. Here we present a small sample of 6 sources
extracted from the fourth INTEGRAL/IBIS catalogue that are still
unidentified/unclassified, but which are very likely associated with a bright,
flat-spectrum radio object. To confirm the association and to study the source
X-ray spectral parameters, we performed X-ray follow-up observations with
Swift/XRT. We report the results obtained from this search and discuss the
nature of each source. 5 of the 6 radio associations are also detected in
X-rays; in 3 cases they are the only counterpart found. IGR J06073--0024 is a
flat-spectrum radio quasar at z=1.08, IGR J14488--4008 is a newly discovered
radio galaxy, while IGR J18129--0649 is an AGN of a still unknown type. The
nature of IGR J07225--3810 and IGR J19386--4653 is less well defined, since in
both cases we find another X-ray source in the INTEGRAL error circle;
nevertheless, the flat-spectrum radio source, likely to be a radio loud AGN,
remains a viable and more convincing association in both cases. Only for IGR
J11544--7618 could we not find any convincing counterpart since the radio
association is not an X-ray emitter.
