  Very recently \citet{XueYQ2019} reported an important detection of the X-ray
transient, CDF-S XT2, whose light curve is analogous to X-ray plateau features
of gamma-ray burst afterglows. They suggested that this transient is powered by
a remnant stable magnetar from a binary neutron star merger since several
pieces of evidence (host galaxy, location, and event rate) all point toward
such an assumption. In this paper, we revisit this scenario and confirm that
this X-ray emission can be well explained by the internal gradual magnetic
dissipation process in an ultra-relativistic wind of the newborn magnetar. We
show that both the light curve and spectral evolution of CDF-S XT2 can be well
fitted by such a model. Furthermore, we can probe some key properties of the
central magnetar, such as its initial spin period, surface magnetic field
strength and wind saturation Lorentz factor.
