  We report the discovery of a synchrotron nebula, G283.1-0.59, associated with
PSR J1015-5719. Radio observations using the Molonglo Observatory Synthesis
Telescope and the Australia Telescope Compact Array at 36, 16, 6, and 3 cm
reveal a complex morphology. The pulsar is embedded in the "head" of the nebula
with fan-shaped diffuse emission. This is connected to a circular bubble of 20"
radius and a collimated tail extending over 1'. Polarization measurements show
a highly ordered magnetic field in the nebula. It wraps around the edge of the
head and shows an azimuthal configuration near the pulsar, then switches
direction quasi-periodically near the bubble and in the tail. Together with the
flat radio spectrum observed, we suggest that this system is most plausibly a
pulsar wind nebula (PWN), with the head as a bow shock that has a low Mach
number and the bubble as a shell expanding in a dense environment. The bubble
could act as a magnetic bottle trapping the relativistic particles. A
comparison with other bow-shock PWNe with higher Mach numbers shows similar
structure and B-field geometry, implying that pulsar velocity may not be the
most critical factor in determining the properties of these systems.
  We also derive analytic expressions for the projected standoff distance and
shape of an inclined bow shock. It is found that the projected distance is
always larger than the true distance in three dimensions. On the other hand,
the projected shape is not sensitive to the inclination after rescaling with
the projected standoff distance.
