Presentation #109.02 in the session IXPE.
The Imaging X-ray Polarimetry Explorer (IXPE) started science operations in January, 2022 measuring polarizations of active galaxies in the 2-8 keV band. Significant detections have been obtained for several blazars with high spectral peaks - where the X-ray band is dominated by synchrotron radiation. For blazars with low spectral peaks (LBLs), the X-ray band is not associated with the synchrotron component but is instead dominated by a second component that is usually identified with Compton scattering by electrons in a relativistic jet along the line of sight. The source of photons for upscattering is uncertain but potentially tested with X-ray polarimetry. Here, we report the IXPE results for four blazars and describe the implications regarding the origin of the X-ray emission from these LBLs. While IXPE has not yet detected polarization from LBL sources, the derived upper limits are already useful in discriminating against some models such as those with strong proton synchrotron components. A technique for searching for and measuring the rotations of electric vector position angles will also be presented, which is generalizable to many sources. IXPE is a joint US and Italian mission. The US contribution is supported by NASA and led and managed by its Marshall Space Flight Center with industry partner Ball Aerospace. The Italian contribution is supported by the Italian Space Agency and its Space Science Data Center and by the Istituto Nazionale di Astrofisica and the Istituto Nazionale di Fisica Nucleare in Italy.