Research On The Optimization Of Front-End Electronics For CXPD CubeSat

Spectroscopy,timing,imaging,and polarization are the four fundamental dimensions of astronomical observation.Among them,observing the X-ray polarization of celestial bodies can provide information that cannot be detected by other dimensions,which is helpful for studying the physical processes and geometric structures of celestial bodies.Gamma-ray bursts(GRBs)are a type of transient source.It has been over50 years since the first detection of gamma-ray bursts in 1967,but questions regarding the composition of their jets,magnetic field structure,and central engines remain unresolved.Studying the X-ray polarization angle and polarization degree of GRBs can help solve the above problems.The POLAR-2is the next-generation space detection facility of China’s POLAR experiment,which can perform high-precision measurements of the polarization state of soft X-rays to gamma rays in GRB radiation.The Low Energy X-ray Polarization Detector(LPD)developed by the Guangxi Key Laboratory for Relativistic Astrophysics in collaboration with domestic research institutes and universities is one of the three payloads of POLAR-2.LPD is used to measure the polarization of GRBs and their early X-ray afterglows,including polarization degree and polarization direction,aiming to solve the unresolved problems of GRBs.The Cosmic X-ray Polarization Detector is a Cube Sat used to fly-validate the technology of LPD and provide technical support for the development and launch of LPD.The paper studies the front-end electronics of CXPD Cube Sat based on the physical requirements of CXPD Cube Sat.It includes a rolling shutter CMOS pixel chip Topmetal-Ⅱ~-and a bottom readout circuit of the microchannel gas electron multiplier(GMCP).Topmetal-Ⅱ~-is used for imaging the photoelectric trajectory to measure the polarization of X-rays,while the bottom readout circuit of GMCP is used to measure the energy and time of incident X-rays.The specific content includes the performance research and testing of Topmetal-Ⅱ~-,such as pixel uniformity and nonlinearity;the design of the GMCP’s bottom readout circuit,which mainly includes a charge-sensitive preamplifier,a filter shaper and a digital circuit;and the performance test of front-end electronics for X-ray polarization source measurement.The front-end electronics has good polarization measurement capability under X-ray polarization sources with energies of 8.0 ke V,6.4 ke V,5.9 ke V and 4.5 ke V.The modulation of track reconstruction can reach 55%under the condition of 8.0 ke V,and the energy resolution can reach 16%.The time accuracy of the GMCP’s bottom readout circuit can reach 19 ns.After two parts of the front-end electronics are matched with the events,the time of Topmetal-Ⅱ~-events can be corrected.The CXPD Cube Sat has been submitted to the satellite company and has passed all necessary performance verification tests before launch.After the tests,the front-end electronics are working normally.