X-ray polarimetry with a conventional gas proportional counter through rise-time analysis

We have performed an experiment on the signal rise time of a Xe gas proportional counter using a polarized X-ray beam of synchrotron orbital radiation with energies from 10 to 40 keV. When the counter anode is perpendicular to the electric vector of the incident X-ray photons, the average rise time becomes significantly longer than that for the parallel case. This indicates that the conventional gas proportional counters are useful for X-ray polarimetry. The moderate modulation contrast of this rise-time polarimeter (M=0.1 for 10 keV X-rays and M=0.35 for 40 keV X-rays), with capability of the simultaneous measuring X-ray energies and the timing, would be useful for applications in X-ray astronomy and in other fields.