White Paper for Blazar Observations with a GEMS-like X-ray Polarimetry
  Mission
  In this document, we describe the scientific potential of blazar observations
with a X-ray polarimetry mission like GEMS (Gravity and Extreme Magnetism
SMEX). We describe five blazar science investigations that such a mission would
enable: (i) the structure and the role of magnetic fields in AGN jets, (ii)
analysis of the polarization of the synchrotron X-ray emission from AGN jets,
(iii) discrimination between synchrotron self-Compton and external Compton
models for blazars with inverse Compton emission in the X-ray band, (iv) a
precision study of the polarization properties of the X-ray emission from
Cen-A, (v) tests of Lorentz Invariance based on X-ray polarimetric observations
of blazars. We conclude with a discussion of a straw man observation program
and recommended accompanying multiwavelength observations.
