Simulazioni di osservazioni polarimetriche in banda X con la missione XIPE Simulations of X-ray polarizations measurements with XIPE

Neutron stars (NSs) and, in particular, ultra magnetized NSs (magnetars) provide a unique scenario to investigate the properties of matter under extreme conditions. All observations made so far were performed in the timing and spectral domain and have not addressed polarization. The ESA XIPE (X-ray Imaging Polarimetry Explorer) mission, which is expected to be launched within 2025, will at last perform polarization measures. This work discusses how polarimetry with XIPE can open a new window in NS astrophysics and allow us to measure quantities that are impossible to estimate otherwise. The focus is on a particular class of NSs, transient magnetars i.e. ultra-magnetized NSs which become bright during outbursts and, in particular, on how polarimetry will be able to determine the geometrical properties of the source (inclination to the line of sight and of the magnetic axis). Furthermore, the possibility of testing “vacuum polarization”, a QED effect never experimentally verified as yet, is discussed. A set of simulated XIPE observations was produced and compared with theoretical models. Results show a good predictive capability in determining the source geometry and that, under favorable conditions, polarimetry can indeed provide a direct test of QED effects.