General History of X-Ray Polarimetry in Astrophysics

Abstract: Soon after the discovery of the first extrasolar X-Ray sources it was suggested that polarimetry could play a major role as a diagnostic tool. Attempts to measure polarization of X-Ray sources was performed by the team of Columbia University lead by Robert Novick. The technique of Bragg diffraction at 45{\deg} was successful to detect the polarization of the Crab with rockets and with OSO-8 satellite. In the following evolution of X-Ray Astronomy, Polarimetry was too mismatched with the improved sensitivity of imaging and spectroscopy, based on the use of optics. As a consequence no polarimeter was flown any more. At the beginning of the century a new class of instruments based on the photoelectric effect were developed. In the focus of an X-Ray telescope they can perform angular, energy and time resolved polarimetry and benefit of the large increase of sensitivity due to the optics. The Imaging X-Ray Polarimetry Explorer, exploiting this technique, was launched at the end of 2021.