Radio Detection of A Candidate Neutron Star Associated with Galactic
  Center Supernova Remnant Sagittarius A East
  We report the VLA detection of the radio counterpart of the X-ray object
referred to as the "Cannonball", which has been proposed to be the remnant
neutron star resulting from the creation of the Galactic Center supernova
remnant, Sagittarius A East. The radio object was detected both in our new VLA
image from observations in 2012 at 5.5 GHz and in archival VLA images from
observations in 1987 at 4.75 GHz and in the period from 1990 to 2002 at 8.31
GHz. The radio morphology of this object is characterized as a compact,
partially resolved point source located at the northern tip of a radio "tongue"
similar to the X-ray structure observed by Chandra. Behind the Cannonball, a
radio counterpart to the X-ray plume is observed. This object consists of a
broad radio plume with a size of 30\arcsec$\times$15\arcsec, followed by a
linear tail having a length of 30\arcsec. The compact head and broad plume
sources appear to have relatively flat spectra ($\propto\nu^\alpha$) with mean
values of $\alpha=-0.44\pm0.08$ and $-0.10\pm0.02$, respectively; and the
linear tail shows a steep spectrum with the mean value of $-1.94\pm0.05$. The
total radio luminosity integrated from these components is $\sim8\times10^{33}$
erg s$^{-1}$, while the emission from the head and tongue amounts for only
$\sim1.5\times10^{31}$ erg s$^{-1}$. Based on the images obtained from the two
epochs' observations at 5 GHz, we infer the proper motion of the object:
$\mu_\alpha = 0.001 \pm0.003$ arcsec yr$^{-1}$ and $\mu_\delta = 0.013
\pm0.003$ arcsec yr$^{-1}$. With an implied velocity of 500 km s$^{-1}$, a
plausible model can be constructed in which a runaway neutron star surrounded
by a pulsar wind nebula was created in the event that produced Sgr A East. The
inferred age of this object, assuming that its origin coincides with the center
of Sgr A East, is approximately 9000 years.
