  Context. GJ 581, an M3 dwarf, hosts a rich system of exo-planets, some of
which are potentially within or at the edge of the Habitable Zone. Nevertheless
the system habitability might be reduced by large and sterilizing high energy
emission flares, if these are frequent. Aims. The GJ 581 radiation environment
was studied with simultaneous X-ray and UV observations, performed with the XRT
and UVOT instruments, respectively, on board of the SWIFT satellite. Methods.
X-ray and UV data were analysed with the distributed standard tools. Results.
GJ 581 was detected for the first time in the 0.2-10 keV range, with an
intensity of (8+-2)x10^{-4} cts/s and a signal-to-noise ratio of 3.6. If
black-body or APEC spectra are assumed then the source X-ray flux is found to
be between 1.8 and 3.3x10^{-14}erg cm^{-2}s^{-1} and log10(L_{X}) between
25.914 and 26.176. Despite hints of X-ray variability, better statistics will
be needed to establish robust evidence for that. The UV measurements, obtained
during 13 pointings, are also reported. A combination of these Swift X-ray and
Hubble Space Telescope UV measurements (with Lyman-alpha) indicate a low X-ray
to UV luminosity ratio of ~4%. Conclusions. Simultaneous X-ray and UV
observations of GJ 581 are reported. These constitute an experimental view of
the system radiation environment, which will be a useful input for the
habitability studies of the GJ 581 planetary system.
