Speaker
Description
X-ray polarization provides unique insights into the geometry, magnetic field configuration, and emission mechanisms of high-energy astrophysical sources. While missions such as PoGO+, Hitomi/SGD, XL-Calibur, and NASA’s IXPE have demonstrated the scientific potential of X-ray polarimetry, there remains a need for instruments capable of simultaneous imaging, spectroscopy, and polarimetry with high spatial and spectral resolution in the medium and hard X-ray bands. We present the development of an X-ray spectro-polarimeter employing fine-pixel CMOS imaging sensors, optimized for the 6–30 keV range, which enables precise tracking of photoelectron trajectories via the photoelectric effect. Two sensor designs have been evaluated: a 2.5 µm pixel CMOS sensor (GPixel GMAX0505) and a 1.5 µm pixel CMOS sensor (Canon LI8020SA). Both offer low readout noise and enable accurate reconstruction of the initial photoelectron direction that encodes the incident photon’s polarization vector. The system is compatible with various optical configurations, such as X-ray reflection mirrors and coded aperture masks, both of which enable high-resolution imaging polarimetry. We have developed a dedicated FPGA-based digital readout and processing system, along with event reconstruction algorithms tailored for X-ray spectro-polarimetric measurements. To demonstrate the concept, beamline experiments using polarized synchrotron X-rays confirm modulation factors consistent with Geant4-based simulations. These experiments also allowed us to evaluate the quantum efficiency and energy resolution of the sensors. This technology offers a compact, low-power, and high-performance platform for future space-borne X-ray polarimeters, scalable from CubeSat-class instruments to larger observatories.
