Presentation #207.06 in the session X-ray Polarimetry Results and Opportunities.
IXPE has completed its first year of measurements of the linear polarization of energetic cosmic phenomena. This talk will discuss IXPE observations of selected radio-loud active galactic nuclei (AGN) with high X-ray fluxes and strong and variable optical polarization (blazars). During the first year of operation IXPE observed a number of AGN, which belong to both sub-classes of blazars, BL Lac objects and quasars. Observations with Swift, NuSTAR, XMM-Newton, and INTEGRAL performed along with IXPE measurements have been used to construct spectral energy distributions of the IXPE blazars over wide X-ray energy ranges. Polarization data at optical, infra-red, and millimeter wavelengths have been obtained simultaneously with IXPE observations. Such multi-wavelength data have provided constraints on the dominant particle acceleration mechanisms in relativistic jets of high synchrotron peak BL Lac objects, while upper limits to the degree of X-ray polarization in low synchrotron peak blazars allow us to exclude some mechanisms for the X-ray production.