Fine pitch CdTe-based hard-X-ray polarimeter performance for space science in the 70-300Â keV energy range

X-rays astrophysical sources have been almost characterized through imaging, spectroscopy and timing analysis. Nevertheless, more observational parameters such as polarization are needed because some radiation mechanisms present in gamma-ray sources are still unclear. We have developed a CdTe based fine-pitch imaging spectrometer, Caliste to study polarization. With a 58-micron pitch and 1 keV energy resolution at 60 keV, we are able to accurately reconstruct the polarization angle and fraction of an impinging flux of photons which are scattered by 90° after Compton diffusion within the crystal. In this paper, we present the principles and the results obtained for this kind of measurements: on one hand, we compare simulations results with experimental data taken at ESRF ID15A (European Synchrotron Radiation Facility) using a 35-300 keV mono-energetic polarized beam. Applying a judicious energy selection to our data set, we reach a remarkable sensitivity level characterized by a measured Quality factor of 0.78±0.02 in the 200-300 keV range; and a measured Q factor of 0.64±0.0 at 70 keV where hard X-rays mirrors are already available.