Active galactic nuclei revealed by X-ray polarization measurements from the Imaging X-ray Polarimetry Explorer (IXPE)

X-ray polarization probes the particle acceleration zone in relativistic jets as well as the geometry of the central region of active galactic nuclei. In its first year of operations, the Imaging X-ray Polarimetry Explorer (IXPE) has completed a first-time characterization of the X-ray polarization properties of a sample of active galactic nuclei. Highlights of these observations include the detection of significant X-ray polarization from the jets of three high-frequency-peaked BL Lac-type blazars (Mrk 501, Mrk 421, and 1ES 1959+650) that point to energy-stratified shocks as the most plausible sites for electron acceleration in jets. The lack of measurable polarization from low-frequency-peaked blazars, on the other hand, constrains the potential contribution from proton synchrotron radiation to the observed X-ray emission. Observations of the radio and Seyfert galaxies have provided constraints on the jet magnetic field and the torus geometry of the central region of active galactic nuclei. This talk will review the IXPE extragalactic program, discussing results from observations of active galactic nuclei and the gamma-ray burst GRB 221009A from which X-ray polarization constraints on the prompt and afterglow emission were derived.