Astronomical X-ray polarimetry based on photoelectric effect with microgap detectors

The polarisation of X-ray photons can be determined by measuring the direction of emission of a K-shell photoelectron. Effective exploitation of this effect below 10keV would allow the development of a highly sensitive X-ray polarimeter dedicated in particular to X-ray astronomy observations. Only with the advent of finely segmented gas detectors it was possible to detect polarisation sensitivity based on the photoelectric effect in this energy range. Simulation and measurements at 5.4 and 8.04keV with a microgap gas counter, using both a polarised and an unpolarised X-ray source, showed that the photoelectron track in a neon-based gas mixture retains the memory of the polarisation of the incoming photons. Possible experiments aimed at galactic/extragalactic sources and solar flares are considered and their sensitivity to these sources is calculated.