CZT focal plane polarimetric performances for Laue lens photons' distributions

To date in astrophysics, X- and gamma-ray source emissions have been studied almost exclusively through spectral and timing variability analysis. However, often two or more distinct models potentially describe the same observations of a particular celestial radiation source. By measuring the angle and degree of linear polarization of the detected radiation, it is possible to double the number of observational parameters, permitting better discrimination between different models. Therefore, future γ-ray telescope instrumentation should incorporate the capability to perform high sensitivity polarimetric measurements. This idea has recently become even more important in the perspective of new very sensitive hard X-and soft gamma-ray focusing missions equipped with CdZnTe focal planes, such as Gamma-Ray Imager and DUAL missions submitted to ESA Cosmic Vision calls. In order to assess the polarimetric performances of a stacked CdZnTe focal plane coupled to wide band-pass Laue optics (100 keV up to 1 MeV) two different sets of independent simulations were performed. Firstly, Laue lens response to different sources (Crab type and monochromatic) was simulated by a Monte Carlo code generating a response photon distribution. Afterwards this distribution was the input of the focal plane mass model simulations, based on GEANT4 toolkit. We have calculated the modulation Q factor and the minimum detectable polarization for on- and off-axis (20′) sources. Polarimetric performances of a CdZnTe prototype operating together with Laue lens crystal samples, tested at the European Synchrotron Radiation Facility, support CdZnTe focal plane simulation data (Q ∼ 0.30 to 0.4, between 200 keV and 600 keV).