Gas microchannel plate-pixel detector for X-ray polarimetry

POLAR-2 is a gamma-ray burst (GRB) polarimeter that is designed to study the polarization in GRB radiation emissions, aiming to improve our knowledge of related mechanisms. POLAR-2 is expected to utilize an on-board polarimeter that is sensitive to soft X-rays (2-10 keV), called low-energy polarization detector. We have developed a new soft X-ray polarization detector prototype based on gas microchannel plates (GMCPs) and pixel chips (Topmetal). The GMCPs have bulk resistance, which prevents charging-up effects and ensures gain stability during operation. The detector is composed of low outgassing materials and is gas-sealed using a laser welding technique, ensuring long-term stability. A modulation factor of 41.28% +/- 0.64% is obtained for a 4.5 keV polarized X-ray beam. A residual modulation of 1.96% +/- 0.58% at 5.9 keV is observed for the entire sensitive area.