Italian Participation to the NASA’s IXPE mission

After my PhD defense, I worked for 1 year at the Institute for Space Astrophysics and Planetology in Rome (Italy) doing research and laboratory activity in the field of high energy astrophysics and X-ray polarisation. I have collaborated with the best experts in X-ray polarimetry in Italy in order to test and calibrate the Gas Pixel Detectors (GPS), the X-ray polarisation detectors which will be placed at the focus of each IXPE X-ray telescopes. I contributed to the first measure of the polarisation of a laboratory source with a continuum energy spectrum, which simulates the effect of a real astrophysical source, carried out with a prototype of the GPD, which is reported in the SPIE proceeding 10699. 

IXPE is a NASA’s Small Explorer program (SMEX) mission. It was announced on 3 January 2017 and launched on December 2021. IXPE exploit the X-ray polarisation from astrophysical sources to provide insight into our understanding of X-ray production in objects such as neutron stars and pulsar wind nebulae, as well as stellar and supermassive black holes. IXPE provides simultaneous spectral, spatial, and temporal measurements of all the observed sources. Some of it’s technical and science objectives include also determining the geometry and the emission mechanism of Active Galactic Nuclei and Microquasars. IXPE will have three identical X-ray telescopes, with polarisation detectors (GPD) at each focus.

GPD are the polarisation detectors based on proportional counters which will detect the polarised light in IXPE. It is an X-ray polarimeter that exploits the photoelectric effect to measure the polarization and to obtain the image of astrophysical sources. The polarised X-ray photon interacts with the gaseous medium and creates photoelectons that are preferentially emitted in the polarisation direction. The photoelectron tracks ionize the gas and an electric field allows electron/ion pairs to drift respectively to the Gas Electron Multiplier (GEM) and top plane. An analysis of the distribution of the initial directions of the tracks gives the degree of polarization and the position angle from the incident X ray.