Spectral and polarimetric characterization of the Gas Microchannel plate Pixel Detector

Abstract

Abstract The Gas Microchannel plate Pixel Detector (GMPD) is used to measure X-ray polarization in astrophysical sources, and is the prototype of the Low Energy Polarimeter Detector (LPD) in the POLAR-2 project. The choice of the detector's gas mixture has a profound impact on its sensitivity to polarized X-rays. Here, we present the characteristics of the GMPD filled with a mixture of 40% He and 60%DME at 0.8 atm. Using Bragg diffraction, we generated nearly fully polarized and monochromatic X-rays at an angle of approximately 45°, and for the first time, we measured the modulation factor and spectral capability at energies of 2.98 keV, 4.51 keV, 6.40 keV, and 8.05 keV. The energy resolution measured is 18% at 6.40 keV, inversely proportional to the square root of the X-ray energy. The measured modulation factors were close to those obtained for the GPD developed by INFN-Pisa and INAF/IASF-Rome, reaching approximately 0.5 above 6 keV, allowing a comparison of the sensitivity of the GMPD and GPD.