  Abridged. We observed the 40 Myr old star DS Tuc A with XMM-Newton and
recorded two X-ray bright flares, with the second event occurring about 12 ks
after the first one. Their duration from the rise to the end of the decay was
of about 8-10 ks in soft X-rays (0.3-10 keV). The flares were also recorded in
the band 200-300 nm with the UVM2 filter of the Optical Monitor. The duration
of the flares in UV was about 3 ks. The observed delay between the peak in the
UV band and in X-rays is a probe of the heating phase followed by the
evaporation and increase of density and emission measure of the flaring loop.
The coronal plasma temperature at the two flare peaks reached 54-55 MK. The
diagnostics based on temperatures and time scales of the flares applied to
these two events allow us to infer a loop length of 5-7 x 10^10 cm, which is
about the size of the stellar radius. We also infer values of electron density
at the flare peaks of 2.3-6.5 x 10^11 cm^-3 , and a minimum magnetic field
strength of order of 300-500 G needed to confine the plasma. The energy
released during the flares was of order of 5-8 x 10^34 erg in the band 0.3-10
keV and 0.9-2.7 x 10^33 erg in the UV band (200-300 nm). We speculate that the
flares were associated with Coronal Mass Ejections (CMEs) that hit the planet
about 3.3 hr after the flares and dramatically increasing the rate of
evaporation of the planet. From the RGS spectra we retrieved the emission
measure distribution and the abundances of coronal metals during the quiescent
and the flaring states. In agreement with what inferred from time resolved
spectroscopy and EPIC spectra, also from the analysis of RGS spectra during the
flares we infer a high electron density.
