Polarized near-infrared light of the Dusty S-cluster Object (DSO/G2) at
  the Galactic Center
  We investigate an infrared-excess source called G2 or Dusty S-cluster Object
(DSO) moving on a highly eccentric orbit around the Galaxy's central black
hole, Sgr A*. We use, for the first time, near-infrared polarimetric imaging
data to determine the nature and the properties of the DSO, and obtain an
improved K_s-band identification of this source in median polarimetry images of
different observing years. The source starts to deviate from the stellar
confusion in 2008, and it does not show any flux density variability over the
years we analyzed it. We measure the polarization degree and angle of the DSO
between 2008 and 2012 and conclude, based on the significance analysis on
polarization parameters, that it is an intrinsically polarized source (>20%)
with a varying polarization angle as it approaches Sgr A* position. DSO shows a
near-infrared excess of K_s-L' > 3 that remains compact close to the pericenter
of its orbit. Its observed parameters and the significant polarization obtained
in this work show that the DSO might be a dust-enshrouded young star, forming a
bow shock as it approaches the super massive black hole. The significantly high
measured polarization degree indicates that it has a non-spherical geometry and
it can be modelled as a combination of a bow shock with a bipolar wind of the
star. We use a 3D radiative transfer model that can reproduce the observed
properties of the source such as the total flux density and the polarization
degree. We obtain that the change of the polarization angle can be due to an
intrinsic change in the source structure. Accretion disc precession of the
young star in the gravitational field of the black hole can lead to the change
of the bipolar outflow and therefore the polarization angle variation. It might
also be the result of the source interaction with the ambient medium.
