Speaker
Description
The Imaging X-ray Polarimetry Explorer (IXPE) provides unique comprehension about polarized x-ray emissions from many astrophysical sources such as radio quiet and radio loud AGNs,galactic black hole binaries and neutron stars. Polarization maps in X-rays of pulsar wind nebulae and supernova remnants have been probed. IXPE has demonstrated the scientific potential of the techniques but revealed some limitations such as, due to the deposition of ions onto the dielectric of Gas Electron Multiplier (GEM) leads towards the decrease in the gas gain. Also, it has arelatively narrow energy band coupled with rapidly declining efficiency. Another limitation of IXPE GPDs was the large dead time (1.1ms), which is incompatible with the brightest sources.Literature showed that 1-cm drift with an 800-mbar dimethyl-ether gas mixture provides the best polarimetric sensitivity. Further optimization of these parameters depends on the mirror's effective area and the energy of x ray source, but no major improvement is expected with current detector design.
So, to overcome all these limitations and better performance, we are developing a next generation 3-D photoelectron track polarimeter based on Gridpix detector with multipurpose ASICs from the Medipix collaboration, Timepix3 and TimePix4. Gridpix structure in principle prevents the buildup of charge on the metallic mesh, offering a small diffusion with respect to GEM. Also, with the Timepix3 we can record Time-of-Arrival (ToA) and Time-over-Threshold (ToT) simultaneously in each pixel. They would also solve the issue of dead time for any planned high-throughput optics. In this work Gridpix detector experimentally characterized at the INAF-IAPS
laboratory using a novel gas mixture of argon (Ar) and dimethyl ether (DME) (80:20). Combining the argon with the low diffusion and precise tracking capability of DME improves the detector performance. To extract key parameters such as energy spectra, energy resolution, and calibration
from raw experimental data demonstrate a good detector response. For the validation of experimental data, a detailed Geant4 simulation is performed. We present the tuning of the simulation to achieve agreement with experimental measurements obtained using a GridPix prototype, highlighting the importance of accurately modeling both the detector response and the reconstruction methods. These results demonstrate the strong potential of the GridPix detector with an Ar:DME gas mixture as a promising candidate for future high-precision X-ray polarimetry
missions.