Remembering Yury N. Gnedin at the Dawn of X-ray Polarimetry: Predictions of IXPE Observations of Neutron Stars

Abstract

NASA’s Imaging X-ray Polarimetry Explorer (IXPE) was launched in December 2021. It is 100 times more sensitive to polarized X-ray emission than any preceding mission and it is opening a new observational window into high-energy astrophysics. I outline Yury N. Gnedin’s many contributions to understanding polarization from neutron stars and present new simulations of observations that IXPE will perform of the X-ray pulsar Hercules X-1 and the magnetar 4U 0141+561 in February 2022. These observations highlight and test particular models that Gnedin and collaborators first proposed. I outline how IXPE will provide unique constraints on the structure and kinematics of the boundary region between the accretion flow and the neutron star surface of Hercules X-1 and how IXPE will verify the predictions of vacuum birefringence for the magnetar 4U 0142+561.