A new technique for measuring the polarization from celestial X-ray sources

The detection of polarized X-rays from cosmic X-ray sources will give useful information about the magnetic fields and matter surrounding these sources. Up to now only one experiment, OSO-8, has measured the degree of polarization from a cosmic X-ray source. In the past we demonstrated a novel new technique using an intensified camera coupled to a gas-filled proportional counter which can be used to measure X-ray polarization by imaging the tracks of photoelectrons ejected when X-rays are absorbed in the detector volume. These tracks contain information about the location of the X-ray interaction point and its polarization. In the lab we have obtained modulation factors of about 30 percent for 60 keV polarized X-rays. Here we discuss preliminary work done towards building a large-area hard X-ray imaging polarimeter which will be able to measure X-ray polarization from bright cosmic X-ray sources at energies between 40 keV and 100 keV.