  Aims. Soft X-ray excesses have been detected in several Be/X-ray binaries and
interpreted as the signature of hard X-ray reprocessing in the inner accretion
disk. The system XMMU J054134.7-682550, located in the LMC, featured a giant
Type II outburst in August 2007. The geometry of this system can be understood
by studying the response of the soft excess emission to the hard X-ray pulses.
  Methods. We have analyzed series of simultaneous observations obtained with
XMM-Newton/EPIC-MOS and RXTE/PCA in order to derive spectral and temporal
characteristics of the system, before, during and after the giant outburst.
Spectral fits were performed and a timing analysis has been carried out.
Spectral variability, spin period evolution and energy dependent pulse shapes
are analysed.
  Results. The outburst (L_X = 3* 10^38 erg/s \approx L_EDD) spectrum could be
modeled successfully using a cutoff powerlaw, a cold disk emission, a hot
blackbody, and a cyclotron absorption line. The magnetic field and
magnetospheric radius could be constrained. The thickness of the inner
accretion disk is broadened to a width of 75 km. The hot blackbody component
features sinusoidal modulations indicating that the bulk of the hard X-ray
emission is emitted preferentially along the magnetic equator. The spin period
of the pulsar decreased very significantly during the outburst. This is
consistent with a variety of neutron star equations of state and indicates a
very high accretion rate.
