Polarized X-rays from a magnetar

The Imaging X-ray Polarimetry Explorer (IXPE), launched in December 2021, has taken the first measurements of soft X-ray (2-8 keV) polarization from a variety of sources, including strongly-magnetized neutron stars (magnetars). In this presentation, we will describe the polarization results from IXPE for two bright magnetars, 4U 0142+61 and 1RXS J170849.0-400910. Furthermore, we will discuss the implications of these results for the complex physics of their surfaces and magnetospheres. We will also discuss these measurements in the context of the expected signatures from QED birefringence and other fundamental physics.