Attività del Dipartimento

Toward a new window in Astrophysics: X-ray Polarimetry

Enrico Costa

Polarimetry is an almost unexplored window of X-Ray Astronomy.
The poor sensitivity of traditional techniques (Bragg diffraction at 45° and Thomson scattering around 90°) resulted in a poor output of pioneering experiments in the ‘70s, polarimetry was not included in all the following missions.
The development of a technique based on the imaging of tracks of photoelectrons absorbed in a gas made feasible a new approach based on an X-ray optics and an imaging detector in the focus. Such a telescope allows to measure simultaneously the position, the time, the energy of the photon and the ejection angle of the photoelectron. From the angular distribution the linear polarization is derived. The whole results in a high sensitivity imaging, timing and spectroscopy polarimeter.
XIPE (X-Ray Imaging polarimetry explorer) is one of the three missions competing as finalist for the Fourth mission of Medium Size of the European Space Agency. It is based on three grazing incidence telescopes with three polarmeters in the focus. It can allow for a dramatic step forward in sensitivity disclosing this window of High Energy Astrophysics.
From the literature almost all fields of High Energy Astronomy will benefit of polarimetric measurements. XIPE will be an observatory open to the community worldwide, capable perform measurements of high significance in a sample from 100 to 200 sources.
I give some hint of the most interesting hot topics to be studied and solved with XIPE.