  SXP 5.05 is a Be/X-ray binary with a neutron star companion located in the
Small Magellanic Cloud. It was first detected in 2013, and later that year, SXP
5.05 underwent a massive optical and X-ray outburst. This outburst dwarfs any
other optical event that has been observed for this system during the last 5
years. The large increase in optical brightness of the system implies an
increase in the size and density of the Be star's circumstellar disc. The X-ray
data show two occultations of the neutron star per orbit and is not consistent
with a neutron star passing behind the Be star, and hence the disc is
responsible for these occultations. In this paper, we model the outburst of
Be/neutron star binary SXP 5.05 as being due to a large increase in mass
ejection by the Be star. The neutron star passes directly through the growing
disc, and it is shown that the resulting obscuration can qualitatively explain
the observed X-ray behaviour of the system. We find the only way to reproduce
the timescales of the observed optical behaviour of the system is to increase
the mass ejection substantially for a short time (<2 orbits) and to decrease
the viscosity during the event. The general behaviour of the observed X-ray and
Ha line emission are also reproduced by the model. However, the inferred mass
ejection and viscosity needed to produce a sufficiently rapid increase of disc
size are both higher than suggested by previous works.
