  The low frequency radio source GLEAM-X J162759.5$-$523504.3 emits pulsed
coherent polarized emission like that of radio pulsars. Yet its period of 18.18
min (1091 s) is hundreds of times longer than those of confirmed radio pulsars,
and if it is a neutron star its mean radiated power exceeds the upper limit on
its spin-down power by more than an order of magnitude. This may be explained
if it is a white dwarf pulsar, with a moment of inertia several orders of
magnitude greater than those of neutron stars. The Lorentz factor of the
emitting charge bunches may be bounded from below by the widths of the temporal
substructure of their radiation. If the emission is curvature radiation, the
radius of curvature may be estimated from the Lorentz factor and the
frequencies of emission; it is consistent with a white dwarf's inner
magnetosphere but not a neutron star's.
