A new photoelectron imager for X-ray astronomical polarimetry

A new photoelectron imager for X-ray astronomical polarimetry (PIAP) has been developed and tested at the Frascati laboratories (LNF-INFN). A charge-coupled device (CCD) is placed on one of the two conjugate foci of a Cassegrain reflective optics onto which are focused UV photons emitted by means of gas scintillation. This X-ray detector has been built to image the angular distribution of the photoelectron tracks, whose anisotropy measures the X-ray polarization. First tests, performed by using mixtures based on argon gas and benzene at low pressure, show events which are candidate tracks of photoelectrons and Auger electrons produced by a Fe-55 source.