Active galaxy unification in the era of X-ray polarimetry
  Active Galactic Nuclei (AGN), Seyfert galaxies and quasars, are powered by
luminous accretion and often accompanied by winds which are powerful enough to
affect the AGN mass budget, and whose observational appearance bears an imprint
of processes which are happening within the central parsec around the black
hole (BH). One example of such a wind is the partially ionized gas responsible
for X-ray and UV absorption ('warm absorbers'). Here we show that such gas will
have a distinct signature when viewed in polarized X-rays. Observations of such
polarization can test models for the geometry of the flow, and the gas
responsible for launching and collimating it. We present calculations which
show that the polarization depends on the hydrodynamics of the flow, the
quantum mechanics of resonance line scattering and the transfer of polarized
X-ray light in the highly ionized moving gas. The results emphasize the three
dimensional nature of the wind for modeling spectra. We show that the
polarization in the 0.1-10 keV energy range is dominated by the effects of
resonance lines. We predict a $5-25%$ X-ray polarization signature of type-2
objects in this energy range. These results are general to flows which
originate from a cold torus-like structure, located $\sim 1$pc from the BH,
which wraps the BH and is ultimately responsible for the apparent dichotomy
between type 1 and type 2 AGNs. Such signals will be detectable by future
dedicated X-ray polarimetry space missions, such as the NASA Gravity and
Extreme Magnetism SMEX, GEMS.
