Polarimetric Imaging of Sgr A* in its Flaring State
  The Galaxy's supermassive black hole, Sgr A*, produces an outburst of
infrared radiation about once every 6 hours, sometimes accompanied by an even
more energetic flurry of X-rays. The NIR photons are produced by nonthermal
synchrotron processes, but we still don't completely understand where or why
these flares originate, nor exactly how the X-rays are emitted. The power-law
electrons radiating the infrared light may be partially cooled, so the
distribution may be a broken power law with a ("cooling break") transition
frequency. In addition, the emission region appears to be rather compact,
possibly restricted to the inner edge of the accretion disk. In that case, the
X-ray outburst may itself be due to synchrotron processes by the most energetic
particles in this population. In this paper, we examine several key features of
this proposal, producing relativistically correct polarimetric images of Sgr
A*'s NIR and X-ray flare emission, in order to determine (1) whether the
measured NIR polarization fraction is consistent with this geometry, and (2)
whether the predicted X-ray to NIR peak fluxes are confirmed by the currently
available multi-wavelength observations. We also calculate the X-ray
polarization fraction and position angle (relative to that of the NIR photons)
in anticipation of such measurements in the coming years. We show that whereas
the polarization fraction and position angle of the X-rays are similar to those
of the NIR component for synchrotron-cooled emission, these quantities are
measurably different when the X-rays emerge from a scattering medium. It is
clear, therefore, that the development of X-ray polarimetry will represent a
major new tool for studying the spacetime near supermassive black holes.
