A VLA Polarimetric Study of the Galactic Center Radio Arc:
  Characterizing Polarization, Rotation Measure, and Magnetic Field Properties
  The Radio Arc is one of the brightest systems of non-thermal filaments (NTFs)
in the Galactic Center, located near several prominent HII regions (Sickle and
Pistol) and the Quintuplet stellar cluster. We present observations of the Arc
NTFs using the S-, C-, and X-bands of the Very Large Array interferometer. Our
images of total intensity reveal large-scale helical features that surround the
Arc NTFs, very narrow sub-filamentation, and compact sources along the NTFs.
The distribution of polarized intensity is confined to a relatively small area
along the NTFs. There are elongated polarized structures that appear to lack
total intensity counterparts. We detect a range of rotation measure values from
-1000 to -5800 rad m$\rm^{-2}$, likely caused by external Faraday rotation
along the line of sight. After correcting for Faraday rotation, the intrinsic
magnetic field orientation is found to generally trace the extent of the NTFs.
However, the intrinsic magnetic field in several regions of the Arc NTFs shows
an ordered pattern that is rotated with respect to the extent of the NTFs. We
suggest this changing pattern may be caused by an additional magnetized source
along the line of sight, so that we observe two field systems superposed in our
observations. We suggest that the large scale helical segments near the Radio
Arc could be components of such a source causing these changes in intrinsic
magnetic field, and some variations in the polarization and rotation measure
values along the NTFs.
