Performance characterization of a hard x-ray photoelectric polarimeter

As part of an on-going program of X-ray polarimeter development at NASA Goddard Space Flight Center, we have built a Hard X-ray Photoelectric Polarimeter (HXPP) designed for astrophysical observations in 10-60 keV band. HXPP’s detection method is based on photoelectric effect and a gas micro-pattern time projection chamber technique. This allows us to tune polarimeter sensitivity to the bandpass of interest by selection of gas type and gas pressure. Here we report on the first experimental results for measuring X-ray signal above 20 keV with HXPP filled with a mixture of 80% argon and 20% dimethyl ether at the total pressure of 2.5 atm.