  Sub-arcsecond radio continuum observations of the Galactic center region at
$\lambda$6 and 2cm reveal a 0.5$^{\prime\prime}$ diameter source with a
shell-like morphology. This source is linearly polarized at a level of 16% at
$\lambda$6cm and has a steep nonthermal spectrum with spectral index 1.6
between $\lambda$6 and 2 cm. The distance to this source is not known but the
large rotation measure value of 3000 rad m$^{-2}$ suggests that G359.87+0.18 is
likely to be located in the inner Galaxy or at an extragalactic distance. We
discuss possible interpretations of this object as a recent supernova, a very
young supernova remnant, a nova remnant, or an extragalactic source. All
possibilities are highly problematic.
