  In Spring 2011 we observed Sgr A*, the supermassive black hole at the center
of our Galaxy, with XMM-Newton with a total exposure of ~226 ks in coordination
with the 1.3 mm VLBI. We have performed timing analysis of the X-ray emission
from Sgr A* using Bayesian blocks algorithm to detect X-ray flares observed
with XMM-Newton. Furthermore, we computed X-ray smoothed light curves observed
in this campaign in order to have better accuracy on the position and the
amplitude of the flares. We detected 2 X-ray flares on the 2011 March 30 and
April 3 which have for comparison a peak detection level of 6.8 and 5.9 sigma
in the XMM-Newton/EPIC light curve in the 2-10 keV energy range with a 300 s
bin. The former is characterized by 2 sub-flares: the first one is very short
(~458 s) with a peak luminosity of ~9.4E34 erg/s whereas the second one is
longer (~1542 s) with a lower peak luminosity of ~6.8E34 erg/s. The comparison
with the sample of X-ray flares detected during the 2012 Chandra XVP campaign
favors the hypothesis that the 2011 March 30 flare is a single flare rather
than 2 distinct sub-flares. We model the light curve of this flare with the
gravitational lensing of a simple hotspot-like structure but we can not
satisfactorily reproduce the large decay of the light curve between the 2
sub-flares with this model. From magnetic energy heating during the rise phase
of the first sub-flare and assuming an X-ray photons production efficiency of 1
and a magnetic field of 100 G at 2 r_g, we derive an upper limit to the radial
distance of the first sub-flare of 100 r_g. We estimate using the decay phase
of the first sub-flare a lower limit to the radial distance of 4 r_g from
synchrotron cooling in the infrared. The X-ray emitting region of the first
sub-flare is located at a radial position of 4-100 and has a corresponding
radius of 1.8-2.87 in r_g unit for a magnetic field of 100 G at 2 r_g.
