A Monte Carlo Study of a 3D CZT Spectroscopic Imager for Scattering Polarimetry

The measurement of the polarization of the highenergy photons from cosmic sources has now become a key observational parameter for understanding the emission mechanisms and the geometry of the active regions involved. Therefore, a mandatory requirement for new instrumentation in this energy regime will be to provide high sensitivity for polarimetric measurements. For several years, our group has studied the performance of CdTe/CZT pixel spectrometer used as a scattering polarimeter. To achieve the required sensitivity in the 100 keV1 MeV range with the next generation of instrumentation, a challenging solution is offered by a broadband Laue lens telescope paired to a spectrometer with very good three dimensional spatial resolution (i.e. 3D spectroscopic imager). This configuration is proposed for the narrow field instrument of the ASTENA mission concept currently under study in the framework of the AHEAD project. Herein, we report on the results of a Monte Carlo study devoted to optimize the configuration and, in particular, the modulation factor (Q) of a 3D CZT detector for scattering polarimetry when placed in the focus of a Laue lens telescope with a passband of 50-600 keV. We also present results on the dependence of Q on the detector geometrical configuration (thickness and pixel/voxel scales), and from various event filters that can be implemented. Finally, in order to assess the reliability of the implemented numerical model, we compare Monte Carlo results with experimental data obtained using different CdTe spectroscopic imager prototypes.