We report the high S/N observation on October 3 , 2002 with XMM-Newton 
of the brightest X-ray flare detected so far from Sgr A* 
with a duration shorter than one hour ( \sim 2.7 ks ) .
The light curve is almost symmetrical with respect to the peak flare , and no significant difference between the soft and hard X-ray range is detected .
The overall flare spectrum is well represented by an absorbed power-law with a soft photon spectral index of \Gamma =2.5 \pm 0.3 , and a peak 2–10 keV luminosity of 3.6 ^ { +0.3 } _ { -0.4 } \times 10 ^ { 35 } erg s ^ { -1 } , i.e .
a factor 160 higher than the Sgr A* quiescent value .
No significant spectral change during the flare is observed .
This X-ray flare is very different from other bright flares reported so far : it is much brighter and softer .
The present accurate determination of the flare characteristics challenge the current interpretation of the physical processes occuring inside the very close environment of Sgr A* by bringing very strong constraints for the theoretical flare models .