The Radio Properties and Magnetic Field Configuration in the Crab-like
  Pulsar Wind Nebula G54.1+0.3
  We present a multifrequency radio investigation of the Crab-like pulsar wind
nebula (PWN) G54.1+0.3 using the Very Large Array. The high resolution of the
observations reveals that G54.1+0.3 has a complex radio structure which
includes filamentary and loop-like structures that are magnetized, a diffuse
extent similar to the associated diffuse X-ray emission. But the radio and
X-ray structures in the central region differ strikingly, indicating that they
trace very different forms of particle injection from the pulsar and/or
particle acceleration in the nebula. No spectral index gradient is detected in
the radio emission across the PWN, whereas the X-ray emission softens outward
in the nebula. The extensive radio polarization allows us to image in detail
the intrinsic magnetic field, which is well-ordered and reveals that a number
of loop-like filaments are strongly magnetized. In addition, we determine that
there are both radial and toroidal components to the magnetic field structure
of the pulsar wind nebula. Strong mid-IR emission detected in Spitzer Space
Telescope data is closely correlated with the radio emission arising from the
southern edge of G54.1+0.3. In particular, the distributions of radio and X-ray
emission compared with the mid-IR emission suggest that the PWN may be
interacting with this interstellar cloud. This may be the first PWN where we
are directly detecting its interplay with an interstellar cloud that has
survived the impact of the supernova explosion associated with the pulsar's
progenitor.
