  Synchrotron X-ray emission from the rims of young supernova remnants allows
us to study the high-energy tail of the electrons accelerated at the shock
front. The analysis of X-ray spectra can provide information on the physical
mechanisms that limit the energy achieved by the electrons in the acceleration
process. We aim at verifying whether the maximum electron energy in SN 1006 is
limited by synchrotron losses and at obtaining information on the shape of the
cutoff in the X-ray synchrotron emission. We analyzed the deep observations of
the XMM-Newton SN 1006 Large Program. We performed spatially resolved spectral
analysis of a set of small regions in the nonthermal limbs and studied the
X-ray spectra by adopting models that assume different electron spectra. We
found out that a loss-limited model provides the best fit to all the spectra
and this indicates that the shape of the cutoff in the electron momentum (p)
distribution has the form exp[-(p/p_cut)^2]. We also detected residual thermal
emission from shocked ambient medium and confirmed the reliability of previous
estimates of the post-shock density. Our results indicate that radiative losses
play a fundamental role in shaping the electron spectrum in SN 1006.
