  The nature of the hard X-ray source XSSJ12270-4859 is still unclear though it
was claimed to be a magnetic Cataclysmic Variable. We here present a broad-band
X-ray and gamma ray study based on a recent XMM-Newton observation and archival
INTEGRAL and RXTE data. From the Fermi/LAT 1-year point source catalogue, we
tentatively associate XSSJ12270-4859 with 1FGLJ1227.9-4852, a source of high
energy gamma rays with emission up to 10GeV. We complement the study with UV
photometry from XMM-Newton and ground-based optical and near-IR photometry. The
X-ray emission is highly variable showing flares and intensity dips. The X-ray
flares consist of flare-dip pairs. Flares are also detected in the UV range but
not the dips. Aperiodic dipping behaviour is also observed during X-ray
quiescence but not in the UV. The 0.2-100keV spectrum is featureless and
described by a power law model with Gamma=1.7. The 100MeV-10GeV spectrum is
instead represented by a power law index of 2.45. The luminosity ratio between
0.1-100GeV and 0.2--100keV is ~0.8, hence the GeV emission is a significant
component of the total energy output. Furthermore, the X-ray spectrum does not
greatly change during flares, quiescence and the dips seen in quiescence but it
hardens during the post-flare dips. Optical photometry reveals a period of
4.32hr likely related to the binary orbit. Near-IR, possibly ellipsoidal,
variations are detected. Large amplitude variability on shorter (tens mins)
timescales are found to be non-periodic. The observed variability at all
wavelengths and the spectral characteristics strongly favour a low-mass
atypical low-luminosity X-ray binary and are against a Cataclysmic Variable
nature. The association with a Fermi/LAT high energy gamma ray source further
strengths this interpretation.
